Linux

Contents

• Introduction
• Basics
• find
• Directories and Files
• Users and security
• Processes, booting (and vmstat)
• Networking
• Scripting
• awk
• tar
• vi / vim
• Regular Expressions
• Miscellaneous, includes history, grep
• Terraform Scripts
• Oracle Specifics
• Mail
• Linux specifics
• FreeNAS
•  

Introduction

Basic Diagnostics

• Are all disks connected (df -k)

Help for Tru64

select instance_name, host_name from v$instance;

Basics

Syntax

Dash '-' in place of an input file indicates standard input and dash in place of an output file indicates standard output

Double dash '--' indicates end of options. Useful for filenames starting with dash: ls -ltr -- -a_file
Another option: ls -ltr ./-a_file

cmd; cmd Semi-colon separates two commands on the same line

Wildcards:
* Zero or more chars except a leading '.'
? Any single character
[aeiouAEIOU] Set
[A-Z] Range
[^set] Matches characters NOT in the set
[!set] Same as previous. For literal ^ or !, don't put as first character
[]set] Literal bracket
[-set] Literal dash first or last
[set-] Literal dash first or last
{a,b,c} Expands to "a b c"
Filename{1,2,3}.txt Expands to "Filename1.txt Filename2.txt Filename3.txt"

~username Expands to user's home directory
~ exands to my home

Excape control characters with ^V, in particular ^V^I gives a tab character.

Look for help

apropos something

Show all entries in the whatis database with something. Same as man -k. search the whatis database for strings

whatis something

Show match based on complete word

man a_command

See manual for a_command
q for quit

more aFile

See file contents. Type h for help.
:n skip to next file
:p go to previous file
:f display current file

which aCommand

Displays the file name of the executable behind a command

which

Show current aliases, and full path

alias

Show current aliases

alias aString

Show the hidden options of a command

alias alias_string='command_string'

Define an alias (BASH, Korn, and C shells)
Examples:
alias cp='cp -i'
alias mv='mv -i'
alias rm='rm -i'

type a_file

Gives file type

a_command --help

On most commands, gives a help page

echo $SHELL

Show which shell I am using

man ascii

Show the ASCII codes. Useful for the control codes.

 

 

 

 

find

find . -name doc

find file doc in directory and sub-directories
Other search operators are:
-iname: case insensitive
-path: search for files in a particular path, with wildcards in path. The argument contains filename in addition to path
-regex: regular expression
-maxdepth n: limit the recursive search to n levels
-mindepth n: extend the recursive search at or beyond beyond n levels
-size:

find . -iname "whatever"

Case insensitive

find . -mtime -1 -print

find changes within last. Remember the minus sign, otherwise it will look for files exactly a day old

find find -print

To find all accessible files whose path name begins with find
question: what difference with or without "print?"

find / -name .profile -print

List all files in the file system with a given base file name

find . -name file\*

Finds all files that have a name starting with file. Notice that the asterisk must be escaped to prevent the shell from interpreting it as a special character.

find . -name file\* -group adm

Finds all files that have a name starting with file and an owning group of adm. Notice that this is the default behavior, and is identical to the next example using the -a operator.

find . -name file\* -o -group adm

Finds all files that have a name starting with file or that have an owning group of adm.

find . -name '*' -mtime -1

find changes within last day. Remember the minus sign. Use single quotes (double quotes seem to work the same way)
find -ctime: creation time

find . -name '*' -mtime +7 -exec rm -f {} \;

Find files changed that are older than a week and remove them. Use single quotes (double quotes seem to work the same way). The curly brackets tell the command that this is where the outcome of the find goes. The escaped ";" indicates the end of the "exec" command
Note that the "exec" spawns a different process for each result of the find command. Try replacing "\;" with "\+", which takes the output of the find command as one long argument. "-ok" instead of "-exec" prompts the user for each result.

find . -name '*sh' -print0 | xargs -0 grep something

Find script files ending in 'sh' and grep for something. Same output as below

find . -type f -exec grep -il something {} \;

Look for regular files and grep for "something". Only show the file names, not the matching content. Same output as below

find . -type f -name "*py" -exec grep -iH something {} \;

Find script files ending in 'py' and grep for "something". List the file names (option H). Option i is for case insensitive

Directories and Files

For viewing files, see further below

cd

to home directory. The tilde ~ also indicates the user's home directory

cd ..

go up

locate filename_or_directory

Searches throughout all the disk. Partial names allowed.
question: what is difference with "find?"

chgrp grp file

change the group ownership of a file

chmod ugo+rwx filename

User, Group, Others(world)
Read, Write, eXecute.
Use - instead of + to remove
-R to apply recursively

chmod go-r filename

Prevent others from reading

chown new_user[:new_group] the_file

Change ownership (generally as root)
-R to apply recursively

cp [-i]

copy files, option i: prompt to overwrite
-p copy with same date
-r copy directory

ls -lt

sort by date, descending

ls -ltr

sort by date, ascending

ls -a

all

ls -l

show details. Depending on first character on the line: d=dir, c=character special device, b=block special device, l=symbolic link, p=named pipe
-F /=dir, *=exec, @=links
-R sub-dir
-t1 Lists all files names with no details, formatted in a single column, newest file first
-b list non-printing characters in \ddd octal notation
-d list only a directory without its contents
-s lists size first, useful for sorting
-c multi-column (default)
-t sort by time of modification
-L list linked file if link
-i Show inode number

fdisk -l

View partitions. Also view partition file: cat /proc/partitions. File systems: cat /etc/fstab and mounted file systems: /etc/mtab.
question: are you sure is it just viewing?

df -k

mount points (~ disks)

df -h

mount points with more usable disk sizes (linux)

ln -s /realpath link

Symbolic link. It's "ln" with "n" followed by "-s"
Without the -s option, it is a hard link.
Remember that hard links cannot link directories and cannot cross file system boundaries, and soft links can.

find . -xtype l 2> /dev/null

Find broken soft links created with ln -s. Optionally use bit bucket so as not to list errors such as denied permission

head -20 file_name

Show first 20 lines of file

tail -20 file_name

Show last 20 lines of file

tail -1 -f file_name

every second, shows all new lines

tail `ls -t1 thread* | head -n 1`

Show the tail of the most recently modified file

du -rk .

disk space used by directory and sub-directories in KB
du -k: KBytes
du -r: Show error if directory not accessible (not on Ubuntu)
du -s: current directory only
du -kr | sort -nr | head -n 20
du -k | sort -nr | head -n 20
du -sk /*: show size of each directory in KB (in the example: root directories)

du -Sht1G *

t1G: Show files larger than 1G
h: human readable size
S: do not include large sub-directories

mkdir

make a directory.
Make many levels in one command: mkdir a/b/c

mv

move or rename files

pwd

Pring Working Directory. Display the pathname of the current working directory

pushd dir

Push directory (not in ksh)

popd

Pop directory (not in ksh)

dirs

Show stack

rm [-i] filename

remove (unlink) files or directories. -i to prompt before deleting

rmdir [-rf] dir

remove (unlink) directories; -rf to remove without warning, including sub-directories

umask

show the permissions that are given to view files by default

zcat

view compressed file (extension Z)

mkdir /mnt/usb-drive
mount /dev/sda1 /mnt/usb-drive

Mount a drive
If the directory /mnt/usb-drive exists and contains files, these files are hidden.
Do not copy on top of a mount point (overwriting the mount point). If something goes wrong, you erase all attached disks

Viewing Files

cat file

display to screen

cat f1 > f2

overwrite

cat f1 >> f2

append to f2

cat > a_file_name

Create a file with input from standard input. End with ctrl-D

cat -vet aFile

Show non-printable characters. ^I is tab; $ is end of line.

cat << END_OF_TEXT_LABEL > a_file_name
something..
something else...
END_OF_TEXT_LABEL

This puts "something \n something else" in a file. Use ">>" when adding to an existing file.
The END_OF_TEXT_LABEL label has to go at the beginning of the line
This construct is called a "here document"

cat -vet a_file_with_null_chars | grep "\^A"

Look for null characters in the file

more

browse or page through a text file, typically do: | more ("pipe" character)
Space: next page, / search, n next occurrence, :n next file.

less filename

Display contents, but with use of arrows up and down

strings aFile

Show user-readable content in aFile

file aFile

display the file type

fsck

umount the file system before running fsck.
Then run fsck /dev/abcd: see man for options. You may want to force a test of bad clusters and verbose output. Fedora: options fv.

If trouble shows up, go into single-user mode (init 1), run fsck several times until no damage is reported, and reboot.

File systems

• ext2: de facto standard on most Linux. Create with mke2fs. Has blocks, inodes and directories
• FFS (Berkeley Fast File System)
• ext3. Create with mke2fs. Allows journaling and fast recovery. Supports POSIX ACL
• FAT32
• HFS
• HFS+
• UFS
• VFAT
• isofs (iso9660): CDROMs

• The superblock is the UNIX equivalent of the Windows File Allocation Table.
• Format a disk with fdisk. Then create the file system, and mount it.
• Mounting a filesystem on a directory hides the files, but does not delete them.
• Disks to be mounted at boot are in /etc/fstab. Format is device name, mount point, filesystem type, options, dump option, fsck option

Comments on NFS (Network File System):
Time stamps are defined by the client, and different clients can have different times
NFS can't do file locking, so each NFS comes with a file locking daemon, for files accessed by several clients. NFS does not know if files are open or closed.

Disk Partitions

• / root
• /swap
• /usr: binaries, kernel source, documentation
• /var: spool directories, error logs
• /tmp: temporary data files
• /boot: kernel images and boot loader configuration
• /home: user home directories

Users and security

id

Gives the user id and the group membership. Also see with:
grep $USER /etc/passwd
Username:password:UID (user ID):GID (group ID):comment:home directory:default shell (/sbin/noloigin if appropriate)
Root is UID 0, system accounts have UID less than 100
grep $USER /etc/group
Account name:password:group ID:member list

useradd -m -s /bin/bash user_name # simplest
useradd -G primary_group -g secondary_group -d /home/usrs/default_dir -m the_new_user

create a new user.
-s defines the default shell
-m creates a home directory
-c "fname the_last_nm" is the full name (optional)
-Gsambashare add to group

usermod ...

Change the user settings

userdel -r the_user

Delete user. -r removes the default directory

groupadd

create a user group

groups a-user

List groups the a-user is in

usermod -a -G <groupname> username

Add a user to a group

usermod -g <groupname> username

Modify a user's primary group

passwd [the_user]

change local or Network Information System (NIS) password information
Some places use yppasswd.
Specify user if it is not the current user

passwd --expire the_user

Force the user to change the password

rlogin host-name

start a login to a different machine. See below

ssh

Secure shell

logout or ctrl-D

Logout of session

su

login as root

su - username

login as "username"

sudo command username
or is it?
sudo -u username command

Execute the command as the user "username"
Note that many people do not login as root but do "sudo command" instead.

runuser - username -c command

Execute the command as the user "username" inside a script.
The script must be run with root

who

Shows who is on the system

w -u

List the process IDs linked to users

w

Shows what users are doing

last [username]

Shows when a person logged on

The /etc/passwd file contents are :
account name : pw placeholder (pw in shadow) : user ID : default group ID : comment : home directory : login shell

Note that if the account name changes but not the user ID, then file permissions are not changed.

The /etc/group file contents are :
group name : pw placeholder : group ID : member list

Edit password file with vipw, edit groups with vigr. Change passwords for groups with gpasswd.

Steps to add a user in Linux (or use the useradd command for adding and userdel for deleting; see useradd.conf file for configuration):

• Add to /etc/passwd file
• Add to /etc/group file
• Create home directory (generally: located at a default home directory, sub-directory is the name of the user )
• Create (copy) the .login or .default files
• Change ownership to user in the user's home directory
• Set initial password
• Use chage to configure password aging (linux).

The command passwd -Sa gives the status of all users. The L means locked, P means a password is set, NP means no password (linux).

Remote Logins

Remote Logins

Create key:
ssh-keygen -t rsa -f ~/.ssh/aName: Creates aName and aName.pub. Share the .pub file. If no name, it generates id_rsa and id_rsa.pub
cp authorized_keys authorized_keys_bkup; cat tmp >> authorized_keys:
ssh -i ~/.ssh/aName username@remotehost
ssh-keygen -f ~/.ssh/id_rsa.pub -m pem -e: Convert from pub format to pem
ssh-keygen -f ~/.ssh/id_rsa -p : Change passphrase

Start ssh agent
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_my

Secure the Server

• Change the WebGUI admin/root user name and password (the default is: admin/freenas)
• Restrict shell access to specific users
• Disable FTP; use SSH or SFTP
• Setup SSH key based authentication
• Always use https protocol
• use SSH tunnel to access webGUI from client to server.
• Owner and group have access, not others
• Access with entering password if username and password match between client and NAS, including case
• Members of the wheel group can sudo if they know the password

See http://phanvinhthinh.blogspot.com/2010/02/how-to-secure-your-freenas-server.html

Copy /etc/ssh/sshd_config and edit:
PasswordAuthentication no # comment out to allow ssh-copy-id
AuthenticationMethods publickey # comment out to allow ssh-copy-id
PubkeyAuthentication yes # comment out to allow ssh-copy-id
PermitRootLogin no
PermitEmptyPasswords no
# other changes, to be confirmed:
ChallengeResponseAuthentication no
UsePAM no
RSAAuthentication yes
# Limit User ssh access: by default, all systems user can login via SSH using their password or public key
AllowUsers chris someone
# restart
systemctl restart sshd


config file:
Host my-ssh-host
  HostName 10.0.0.5
  Port 22
  User myuser
    IdentityFile ~/.ssh/thekey # Not the .pub file, but the secret key file
    IdentitiesOnly yes


Processes

ps $$

Show current login shell
Note: options preceeded by a dash are UNIX/Linux style, options without a dash are BSD style

ps

All my processes

ps ax / ps -A

All processes

ps -ef

HP-UX

ps -f -u a_user

All processes for a particular user a_user (this works on linux)

ps -ef

All processes (this works on linux)

ps -uuser1,user2

Processes linked to users user1 and user2

ps -t console

Processes linked to a console

ps -o pid,user,stat

Show pid, user and stat columns

ps -a

all processes

ps g

all processes

ps l

more details: ppid, cp, pri, nice, vsize, rssize and wchan.

ps -u username

all processes for a user

ps u

user-oriented output: user, pcpu, pmem, vsize, rssize, and start.

ps v

virtual-memory-oriented output: cputime, sl, pagein, vsize, rssize, pcpu, and pmem.

ps aux

Best ???

ps aux | grep abc
pgrep abc

Look for a specific process

ps aux | grep bash

Look for bash shells, typically open terminal windows

ps x

also processes without terminal

pstree

Show tree of process dependencies

top
monitor

Top memory consumers

free -m

Show available memory

vmstat

Show swap space

kill

send a signal to a process, or terminate a process

kill -9

First use ps to see processes

Nice values from -20 to 19. 0 is default. -20 is highest priority. A "nice" process is a process that is nice to others and is willing to wait more.

renice 0 pid

Put back to default 0 priority

renice +1 pid

Lower priority

renice -1 pid

Higher priority. Sudo may be necessary.

renice -n -2 pid

Set to nice value of -2 (more agressive)

Nice values from -20 to 19. 0 is default. -20 is highest priority.

kill pid

Stop job

kill -9 pid

Stop harder

kill -STOP pid
kill -CONT pid

Temporarily stop a process (it is not killed)

pkill firefox

Stop all processes with "firefox"

ps aux | grep Xorg
sudo kill -9 pid-of-Xorg
# or pkill -9 Xorg ???
sudo init 5 # this goes back to graphical interface

This stops the graphical interface.
You may have to do sudo init 3 first

Tru64

ps -A -o pmem,pid,rss,command | sort -nr | head -20

Memory in %, process ID, resident memory, command, sorted

ps -A -o vsz,pcpu,time,user,nswap

Virtual memory size, percent CPU, total CPU used, username, swapping

ps -A -o pmem,pid,rss,vsz,pcpu,nswap,time,stime,user,command | sort -nr | head -20

Useful on Tru64

#!/usr/bin/ksh
ps -A -o pcpu,psr,pmem,rss,vsz,nswap,pid,time,stime,user,command | head -1
ps -A -o pcpu,psr,pmem,rss,vsz,nswap,pid,time,stime,user,command | grep -v "\%CPU" | sort -nr | head -10
echo
ps -A -o pmem,rss,vsz,nswap,pcpu,psr,pid,time,stime,user,command | head -1
ps -A -o pmem,rss,vsz,nswap,pcpu,psr,pid,time,stime,user,command | grep -v "\%CPU" | sort -nr | head -10

Even better on Tru64: it shows processes by CPU consumption and memory consumption. The header is shown.

swapon -s (with root)

swap

?? box at hbsp:
ps -o pcpu,vsz,ruser,pid,ppid,nice,time,tty -A | sort -n

vmstat n s

Virtual memory statistics. Repeat every s seconds, for n times. First line is since boot.

iostat n s

I/O statistics. No other options.

vmstat -i
vmstat -w
vmstat -r

Show statistics, choice of different sets of columns

vmstat -P

Breakdown of page use

vmstat -p s n

Show statistics every s seconds, for n times

vmstat -s

Accumulated statistics

Explanation of columns for "vmstat n s" (first line is since boot):

active pages

In use but can be used for paging

wired pages

In use but cannot be used for paging

inactive pages

Could be used for paging

free pages

Free pages ready for use

reattach / react

Use a page from the inactive list

cow

Copy-on-write page fault: a child process needs a page for writing, so a copy is made.

page in / pin

Number of page requests

page out / pout

Number of pages paged paged out. If constantly over 20, then a lot of paging is happening. Look at io too. A lot of io means a lot of paging.

us sy id iowait

CPU information: us = user and normal processes; sy = system time; id = idle time; iowait = % of iowait.

View uptime by looking at this file: cat /proc/loadavg

Booting

Lilo's purpose is to start up the second stage loader. See /usr/doc/lilo for doc. The configuration is in /etc/lilo.conf

The next step is loading the kernel. Then the init program is run. The init reads the /etc/inittab file. Typically, the inittab will first tell the init program to run the initialization script such as /etc/init.d/rcS for Debian. Then the scripts for each run-level are executed. The filesystems in /etc/fstab are checked (fsch) and mounted (mount).

The inputrc variable says which inputrc program to use to input from the keyboard. The .inputrc could be in the user's home directory, in /etc/inputrc or it could point to /etc/profile.

Shutdown / Boot

shutdown -h now

shutdown button on the left to power off

shutdown -r now

reboot

>>> b

boot

systemctl suspend

Suspend (remember to keep the power cord in, otherwise it will act as if it crashed)

man init; man inittab: specifics for startup/shutdown

Set up terminal (put in .profile, or whatever):

• stty erase "^H" kill "^U" intr "^C" eof "^D" # Set terminal type
• stty erase "^H" configures the backspace key
• eval ` tset -options ` # Set device dependent terminal type and return the type
• set -o vi access to history with the esc+k keys
• set filec auto-complete filenames with esc+esc.
  Note: auto-complete on ksh with set -o vi is esc+\ and auto-complete on bash is tab.

init

/etc/inittab: format is unique ID : run levels : action : process
Levels are:

• 0 - halt
• 1 - single user mode
• 2 - Multiuser, without NFS
• 3 - Full multiuser mode
• 5 - Full multiuser and X11
• 6 - reboot

The /etc/rc.d directory has the configurations of each run level. See runlevel with runlevel. The symbolic links with K correspond to processed that are stopped, and symbolic links with S correspond to those that are started. Do ./xyz status to see if one of them is running

Get out of the graphical interface (GUI):sudo init 3

Log files

• /var/log/messages: main Linux system log
• /var/log/boot.log: Details of last boot
• /var/log/secure: security related

Other

who

users who are logged on

nohup command &

Allow a process to continue to run in the background even though the calling user has logged out (no hangup)

Scripting

Simple script:
Simple script (the #! is called a shebang (from sharp-bang) and indicates that the file is a script. The operating system will try to execute it using the interpreter specified by the rest of the first line.
Colon or ":" is no-op command, and can be found as the first line in a Bourne shell script. So, it should correspond to a valid interpreter. Be careful when moving to a new machine.)
See /bin/sh --help for flags
#!/bin/bash
TXT="Hello World"   # No spaces around the equal. Surround the value with quotes if there are spaces in the string. See more in "variables" below.
set -e: scripts stop on error
set -x: each command is echoed

Execute with:
  ./script_name
Note that execute permissions may have to be set:
  chmod u+x script_name
Run in the background:
  ./script_name &
List background jobs with:
  jobs
Stop a foreground job with ^Z.
Put a stopped job in the background with:
  bg %1

Single quotes and double quotes are used to surround strings. However, variables expand in double quotes (hence the term partial or weak quoting) and do not expand in single quotes (full or strong quoting).
Double quotes protect all special characters except $, ` (backquote), and \ (backslash, used for escape). Also ! for history substitution in C shell.
Single quotes suppresses filename and variable substitution
Back quotes "`" is command substitution

Separate commands on the same line with ";"
Continue a command to the next line with \
The colon (:) is a null command (does nothing).

CommandA && commandB: commandB executes only if commandA is successful
CommandA || commandB: commandB executes if commandA failed.
Therefore, [ a_cond ] && commandB is equivalent to : if [ a_cond ]; then
commandB
fi

Zero before the number means octal notation (012)
Zero X before the number means hexadecimal notation (0xA23D)
nn# before the number means nn base (binary: 2#1001001001)

Eventually put in production in /usr/local/bin

Comments with #. But this may be escaped with " ' or \ (double quote, single quote or backslash) or certain pattern matching expressions.

Redirection:

• Redirect stdout to file: cmd > file
• Redirect stderr to file: cmd 2> file
• Redirect stderr to stdout: cmd 2>1
• Redirect stderr and stdout to file: cmd &> file
• Redirect stdout and stderr to single file: cmd > file 2>&1
• Redirect stdout to one file and stderr to another: cmd > file 2> file_err
• Make the output disappear by redirecting to the bit bucket: cmd > /dev/null
  Redirect the stderr too: >/dev/null 2>&1
  Some shells use a different syntax: >& /dev/null
• Redirect all in the script: exec 1> $0.log 2> $0.err

Startup files

Question: find equivalent for the other shells

set prompt = `hostname`':\!)'   # (not sure about this one: see PS1 below)
set prompt = `hostname`'-'`whoami`':\!)'
alias rm "rm -i"
alias mv "mv -i"
alias cp "cp -i"
alias ll 'ls -la'
alias ls "ls -F"

In BASH, Bourne, and Korn: export PS1=`hostname`'('`whoami`'):$PWD-> '   # $PWD is the current directory (Korn shell)

• TXT="Hello World"   # No spaces around the equal. Surround the value with quotes if there are spaces in the string. See more in "variables" below.
• export ${TXT} # Environment variables have to be exported to be used in another child script
• Use capitals for EXPORTED VARIABLES and lower case otherwise
• 1 to 20 characters, alphabetic, numeric, or underscore. First characters must be alphabetic or underscore. Typically uppercase, especially environment variables (the exported ones).
• Surround string variables with double quotes so that "$A_STRING" is interpreted as an empty string in case the variable is empty, especially in if [ ... ].
• Surround the variable name with curly brackets ${A_VAR} when (1) concatenating the variable with a string and (2) when using a substitution or assignement operator.
• echo "${TXT}": make it a habit to enclose with double quotes and curly brackets
• [local] A_VARIABLE=value  #Defines a variable local to a function
• TO_BE_NULL=  # Set to null
• set   # See values of all variables
• env (or env)  # See values of all environment variables
• unset A_VAR   #unset a variable
  
• No need to declare the type
• $1 is the first argument passed to a function, $2 is the 2^nd, ${10} is the 10^th. The command shift n moves all the arguments down n positions, but the first n arguments are lost.
• $0 is the name of the command from the command line
• $# is the number of parameters
• $? refers to the return value of the previous command
• echo $((1+2)) # evaluate an expression
• echo $[1+2] # evaluate an expression
• $# gives the number of arguments received
• $* and $@ give all the arguments. $* must be quoted ("$*"). In $@, each parameter is a quoted string. "$@" is the best option for passing arguments to another script (in a wrapper for example); remember the double quotes
• Get the last argument (to be verified): args=$#; lastarg=${!args}
• $$ holds the process ID
• $- gives flags passed to the script
• Command substitution: $(commands) expands to the output of the commands
• set a_var = (list of space-separated words)
• $a_var[n] nth item
• $a_var all items
• $a_var[n-m] range of items
• $#a_var count of items
• i=`expr $i + 1`: increase counter. Remember to include spaces between terms and operators.
  Escape multiplication and division operators: \* and \/
• let a_var=$a_var+1# BASH or Korn shell. Remember: no spaces
• Special variables: $HOME Home directory
  $LOGNAME;$USER login name
  $PATH The path variable
  $SHELL Path to shell
  $PWD Current directory
  printenv See all environment variables
• Set a default, meaning that aValue is used if the_var is not yet defined: the_var=${the_var:-aValue}

Escaping

• \n newline
• \r return
• \t tab
• \v vertical tab
• \b backspace
• \a "alert" (beep or flash)
• \0xx octal ASCII equivalent of 0xx
• \" double quote inside a double-quoted string
• \$ dollar sign, so as not to output a variable
• \\ literal backslash
• \ use at the end of a line to continue the command on the next line (it escapes the newline character)

Syntax:

switch (word) 
case str1: 
  breaksw 
case str2: 
  breaksw 
default: 
  breaksw 
endsw

case value in  
  str1)  
    ;; 
  str2|str3)  
    ;; 
  [abc])  
    ;; 
  wildc*rd)  
    ;; 
  *) #otherwise 
    ;; 
esac

case expression in  
  pattern) 
    ... 
    ;; 
  pattern)  
    ... 
    ;; 
  *)  
    # default 
    ;;  
esac

Technically, the "[expression]" is a command and the exit status is the condition. If the exit status is 0 then the following statement is executed. The left bracket is a dedicated command. Therefore, "if command" can be used too. However, double left brackets "[[" is a keyword (bash 2.02) and allows more extended tests.

Another construct is "if ((expr))". The (( )) evaluates and arithmetic expression. Note that (( 0 )) returns 1 and is considered false and (( 1 )) returns 0 and is considered true.

Best practice is to surround the variables with curly brackets and double quotes as in:
if [ "${1}" = "" or "${2}" = "" ]
if [ "${AP_BASE}" = "" ]
Best is to use the test operators -n (non-zero-length string) and -z (zero-length string) instead of comparing to "":
if [ -z "$1" ]; then
   echo 'Usage $0 argument'
fi

Loop example:
i=1
while [ $i -lt 9 ] ; do
  i=`expr $i + 1`
done

The test expression needs spaces around the operator (do NOT write "a=b" but "a = b").
The "[" is an alias for the test command (you can do man test).
When comparing strings, add a character in each one: if [ "x$the_variable" = "xsomething" ]
List of operators (see man test for shell-specific operators):

• [ -n $X ] true if $X has non zero length
• [ -z $X ] true if $X has zero length
• [ -d $DIR ] true if directory $DIR exists
• [ -f $F ] true if file $F exists (as a "regular" file)
• [ -e $F ] true if file $F exists. Note, there are many operators for file existence.
• [ $A -eq $B ] true if $A and $B are integers and they are equal
• [ $A -neq $B ] true if $A and $B are integers and they are NOT equal
• [ $S1 = $S2 ] true if $S1 and $S2 are equal as strings
• [ $S1 != $S2 ] true if $S1 and $S2 are NOT equal as strings
• [ $A -lt $B ] true if $A < $B (both operands should be integers)
• [ $A -gt $B ] true if $A > $B (both operands should be integers)
• [ $A -ge $B ] true if $A >= $B (both operands should be integers)
• [ $A -le $B ] true if $A <= $B (both operands should be integers)
• [ $f1 -nt $f2 ] true if $f1 is newer than $f2
• [ $f1 -ot $f2 ] true if $f1 is older than $f2
• [ "$expr1" -a "expr2" ] true if $expr1 and $epxr2 are true
• [ "$expr1" -o "expr2" ] true if $expr1 or  $epxr2 are true

Korn shell:  if [ .... ]:

• -r file : file exists and is readable.
• -w file : file exists and is writable.
• -x file : file exists and is executable.
• -f file : file exists and is a regular file.
• -d file : file exists and is a directory.
• -s file : file exists and has a size greater than zero.
• -h file : file exists and is a symbolic link.
• -z s1 : true if length of string is zero.
• -n s1 : true if length of string is non-zero.
• s1 = s2 : true if strings s1 and s2 are identical.
• s1 != s2 : true if strings s1 and s2 are not identical.
• s1 : True if s1 is not the null string (my 2 cents: be more explicit and use an operator).
• n1 -eq n2 : True if the integers n1 and n2 are algebraically equal. Comparisons: -ne, -gt, -ge, -lt, and -le
• ! : Unary negation operator.
• -a : Binary AND operator (higher precedence than -o).
• -o : Binary OR operator

This list may be different for [[...]] (see man ksh, under "Conditional Expressions"):

• -a file : True if file exists.
• -d file : True if file exists and is a directory.
• -f file : True if file exists and is an ordinary file.
• -h file : True if file exists and is a symbolic link.
• -L file : True if file exists and is a symbolic link.
• -n string : True if length of string is non-zero.
• -r file : True if file exists and is readable by current process.
• -s file : True if file exists and has size greater than zero.
• -w file : True if file exists and is writable by current process.
• -x file : True if file exists and is executable by current process. If directory, then process has permission to search.
• -z string : True if length of string is zero.
• file1 -nt file2 : True if file1 exists and is newer than file2.
• file1 -ot file2 : True if file1 exists and is older than file2.
• file1 -ef file2 : True if file1 and file2 exist and refer to the same file.
• string = pattern : True if string matches pattern.
• string != pattern : True if string does not match pattern.
• string1 < string2 : True if string1 comes before string2 based on ASCII value of char
• string1 > string2 : True if string1 comes after string2 based on ASCII value of char
• exp1 -eq exp2 : True if exp1 is equal to exp2.
• exp1 -ne exp2 : True if exp1 is not equal to exp2.
• exp1 -lt exp2 : True if exp1 is less than exp2.
• exp1 -gt exp2 : True if exp1 is greater than exp2.
• exp1 -le exp2 : True if exp1 is less than or equal to exp2.
• exp1 -ge exp2 : True if exp1 is greater than or equal to exp2.
• (expression) : group expressions.
• ! expression : True if expression is false.
• expression1 && expression2 is true : True, if expression1 and expression2 are both true
• expression1 || expression2 : True, if either expression1 or expression2 is true

for i in $( ls ); do   # the variable $i takes values in the list
     ...
     if [ ... ]; then break; fi
done

COUNTER=0
while [ $COUNTER -lt 10 ]; do
    ...
    let COUNTER+=1
done

COUNTER=0
until [ $COUNTER -gt 10 ]; do
    echo COUNTER $COUNTER
    let COUNTER+=1
done

case ${the_var} in
   "MED"|"TMT" )
     echo "must ..."
     return 1
     ;;
   "a" )
     echo "OK"
     ;;
   * )
     echo "Valid parameters are ..."
     return 1
     ;;
esac

function fctn_name {
   echo $1
}

echo -n   # -n does not break the line

exit n   # exits the script with exit code n, with 0 meaning successful, 1 to 255 meaning error. If no argument then the exit status of the last command is returned. Note that some exit codes have special meanings, but there is no "official" list.

OPTIONS="list of words"
select opt in $OPTIONS; do   # This prompts the user to choose one of the options. Needs exit option.
    ...
done

echo Please enter ...
read VAR_NAME VAR_NAME_2   # Prompts user to enter a value / input from command line
Use stty -echo; read DB_PWD; stty echo for passwords

Command substitution:
$(commands) expands to the output of the commands. Nesting is possible. Newline characters are not possible.
`commands` expands to the output of the commands (the characters ` is referred to as "back tick"). Newline characters are not possible.
Example: base_list=`cat /etc/oratab | grep -v "#" | awk -F\: '{print "-"$1"-"}'`

Script for user input of options (tldp.org)
Not yet tested
#!/bin/bash
OPTIONS="cmd1 cmd2 x"
select opt in $OPTIONS; do
    if [ "$opt" = "cmd1" ]; then
        ...
    elif [ "$opt" = "cmd2" ]; then
        ...
    elif [ "$opt" = "x" ]; then
        exit
    else
        echo Option "$opt" not known
    fi
done

Sample wrapper for calling another script

Infinite loop:
while :; do
echo infinite loop (remember to put an exit condition!!)
done

awk

ls -lt udump | awk '{print "ls -l "$9}' > a_file

print rm followed by 9th column (file name). Run a_file then :%s/^ls -l/rm/
$0 returns the whole line (to be tested)

awk -F\t '{print $2, $3}' the_file

Show the second and third columns of a tab-delimited file

awk '{print $3}' | sort -u

Sort the third column and eliminate the duplicates

awk '$1 == "something" {print $1, "|", $3}'
awk '$1 ~ /^something$/ {print $1, "|", $3}'

Two ways to look for rows where first column is equal to something.
In the output, separate the two columns with a vertical bar.

awk '$1 !~ /^$/ {print $1, "|", $3}'

Look for rows where first column is empty.

awk '{print $1","$2",\""$3"\",\""$4"\""}' a_file > a_csv_file.csv

Create a comma-separated-version file. The last two columns are surrounded by double quotes.

awk '{print $1"\t"$2"\t"$3"\t"$4}' a_file > a_tab_delim_file

Create a tab-delimited file.

awk '{print substr($0, 10, 30)}' a_file

Substring, here substring of the whole line.
substr($0, n [, m]): n is the start position (1 is left-most), m is the optional length

awk -F"\t" -v OFS="\t" '{print FILENAME,$0}' file_in > file_out

input tab-delimited, output tab-delimited (OFS = specifies output delimiter)

awk -v var_name=${a_variable} '{...}'

Assign a variable for use within the awk command

ls -la | awk -F"/" '{print $NF }'

Get the file name without the path. $NF is the last "column"

cook book / Fre

grep "package succeed" thread* | awk '{print $6":"$10 }' | awk -F":" '{print $1 $2}' | sort -u
grep "package fail"    thread* | awk '{print $6":"$10 }' | awk -F":" '{print $1 $2}' | sort -u

Processes that succeeded with the hours

awk '$3 == "package" {print $4":"$6":"$10 }' thread* | awk -F":" '{print $2, $1, $3}' | sort -u

Processes, success/failure, and hour

awk '{print substr($0, 20)}' a_file | sort -u

List distinct values of lines starting with 20th character

awk '{ sub("\r$", ""); print }' dos_format > unix_format

Get rid of the CR at the ends of the lines

awk 'sub("$", "\r")' unix_file > dos_format

Change LF into CRLF

awk -F"|" '{print $1 " " $2}' dmrt_xxx.ext | sort -u

Get a distinct list of the fac ID and P.A.N. (MRN is $51 in pat)

awk -F"|" '{print $51, $2, $1}' the_file

Show a subset of the columns in a pipe-delimited file

awk -F"|" '$51 == "(10 spaces)" {print $1 " " $2 " " $51}' the_pat_file

Rows with empty MRN

 

 

 

 

Documentation:

• The GNU Awk User's Guide

Networking

ifconfig [-a] [-v] [interf]

Network configuration, a for all, v for verbose. Lists interfaces. "interf" can be eth0, lo, ...

ip addr

IP addresses

netstat [-i]

Summary of interfaces

ping -c n

n is number of packets to be sent

traceroute

traceroute6 for IPv6

tracepath ip-or-name

On Linux, similar to traceroute

mtr ip-or-name

On Linux, combines traceroute and ping

host ip-or-name

On Linux, gives IP address, or, for IP address, gives hostname

ifplugstatus [eth0]]

On Linux, gives status of the interfaces. A message like "link beat detected" means plugged in, otherwise, a message like "unplugged"
(install with sudo apt-get install ifplugd)

route -n

 

netstat -anp

All sockets, numeric display, display pid

netstat -nr

Display in numeric output, display routing table
Option a for all open ports
Option l for listening ports

netstat -a

find all open ports

/etc/inetd.conf
/etc/services

Files to help find open ports

See /etc/sysconfig/network. This is where the hostname is defined.
Each interface has a configuration file in /etc/sysconfig/network-scripts.

Restart network: /etc/init.d/networking restart

See the hostname: execute /bin/hostname or look at file /etc/hostname

Address lookups (host file): /etc/hosts
The file /etc/resolv.conf points to a specific server for name lookups (dns servers). In the case of a router, the address of the router would be in this file.

Samba

The Samba configuration is in /etc/samba/smb.conf
Restart Samba server after changing the configuration: /etc/init.d/samba restart
To install, use the Synaptic Package Managger and search for Samba.
Query the Samba server: smbclient -L ubuntu -U% (Replace the % with a username to see what a specific user will see.)

tar

-c --> create
-r --> write at end of archive
-t --> list contents
-u --> add files to tape
-x --> extract
options:
-b : block factor (block size) for tapes
-e : exclude
-f : tar file name
-v : verbose

examples:

tar cvf /dev/ntape/tape0 -e ./foo $HOME

create a tar on tape with $HOME, exclude ./foo

 

tar cvf the_file.tar sub_dir/*

create a tar with all of the sub-directory sub_dir

 

tar -xvf abc.tar

extract the contents of the tar.

tar xvf -C dir abc.tar

extract the contents of the tar to the "dir" directory (verify).

compress *.tar
uncompress *.z
Other utilities: zip
zip a_file gives a_file.gz (tar directories before gzip)
zip -d a_file.gz decompresses

vi

Configuration in .exrc in home directory
In vim, do :edit $MYVIMRC. Locations shown in :version.
See variable values with :echo $VIM and :echo $HOME
Try C:\users\the_user\_vimrc or ...\gVimPortable\Data\settings\_vimrc.

Insert

Moving

Deleting

Searching

Advanced Editing

EX commands, including setting parameters and exiting

Some vim tips

• * searches for the word under the cursor
• Improve searching with "incsearch" and "hlsearch" options
• :be xterm --> set selectmode to "", mousemodel to "extend", keymodel to "", and selection to "inclusive"
• :set slm=cmd / :set selectmode=cmd --> use v, V, ^V to start selections
• :set selection=exclusive / :set sel=exclusive Exclude character under cursor in visual selections
• :set ic --> ignore case when searching
• v(move)operator, where operator can be c, d, y, gu (lower case), gu (upper case)
• :n $VIM or :echo $VIM Shows variable $VIM
• $VIM --> C:\Program Files\Vim
  ~ = $HOME --> C:\Documents and Settings\the_user
• :set ff=unix or :set ff=dos: define the file format, more specifically define the end-of-line character. You can read in one format and write in the other.
  
• If I see ^M in the text, check to see if the file format (:set ff). If it is "dos", then the ^M means there are CR / \r / chr(13) characters without a LF / \n / chr(10) after them. This worked: :%s/\r/\r\n/g. This gives a ^@ character at the beginning of the line. Search for it with /\%o0 (backslash % lowercase letter o zero). Remove with :%s/\%o0//g.
Note: to edit binary files, start vim with the -b option (I have not tested it yet).
• ggVG: select all
• :set nu / :set nonu Show or hide the line numbers
• :set wrap / :set nowrap Line wrap
• :set list / :set nolist Invisible characters. EOL=$
• :set noautoindent / :set noai Auto-indent
• :set noshowmatch / :set nosm Brief jump to matching brackets when inserting
• :set expandtab / :set et / :set noet Replace tabs with spaces. Insert real tab with ctrl^V
• :set indentexpr="" Defines how the indents are calculated. The directive does not work in the vimrc file, so type :set indentexpr=""
• :set tabstop=4 shiftwidth=4 expandtab Advance 4 spaces when pressing tab or ">". Replace existing tabs with spaces: :retab
• :set tabstop=4 shiftwidth=4 expandtab
• :highlight Comment ctermfg=green guifg=greenChange the practically illegible blue to green for comments
• :set t_Co=0: turn off color terminal. Use this when the syntax highlighting scheme makes the text unreadable.
• :set tabstop=4 shiftwidth=4 expandtab autoindent showmatch nowrap Best for editing Python scripts

Modify multiple files:
vi *html # or whatever wildcard is appropriate
:bufdo %s/look-for/replace-with/ge | update

Sample vimrc file:

set lines=40
set columns=150
set ignorecase
set noautoindent
set indentexpr=""
set expandtab
set noshowmatch
set backup
set backupext=.bak
set patchmode=.orig.txt


Portable version
Execute with C:\progfile\papps\gVimPortable\App\vim\vim73\gvim.exe
vimrc in "C:\progfile\papps\gVimPortable\Data\settings\_vimrc"

Macros

For macros in vim, see below. Consider using the macro function in reflexion too.

To record a macro

• Press qc, where c is a lower case character to name the macro
• Edit file
• Press q to end recording

Play back the macro

• Press @c, with c as the character above
• To repeat multiple times: NN@c, where NN is a number

Regular expressions

Alphanumeric characters stand for themselves. Prefix other characters with \ if needed.

See www.regular-expressions.info (explore some more)

Examples:

Misc

echo

echo arguments to the standard options

grep str filename

search a file for a string or regular expression
Surround "str" with double quotes if there is a space, or single quotes if there is a special character such as $, *, [ or other. The filename can have a wildcard
^ = beginning of line ; $ = end of line; . = single char; \ escape the following char
-i ignore case
-n line number
-l list files
-v lines that do not contain the string
-h Do not display filenames when searching multiple files.

sort -nr filename

-n interpret first field as numbers
-r reverse order
-u eliminate duplicate lines
-o give file for output

uniq in_file out_file

eliminates consecutive matching lines
-d gives ony the duplicate lines
-c give count of duplicate lines

cut -c list [file ...]

Extract based on character position.
cut -b for byte position (equivalent to -c option for single-byte character sets)
list of positions: 1,4,7 = pos 1, 4, and 7; 1-3 = pos 1 to 3; -5 = pos 1 to 5; 3- = pos 3 to last

cut -f list [-d char] [-s] [file ...]

Extract based on field delimiter char. List is same as for cut -c. Put quotes around char if it has a special meaning. Default is tab.
Option -s to suppress output of lines with no delimiters
cut -f 2-4 -d: get columns 2 to 4 defined by colon as a delimiter
grep something * | cut -f 1 -d: | sort -u tidy up grep output

paste -d list file1 file2

Merge the two files on a line by line basis, with [line from file1][delimiter][line from file2]
The delimiter is tab by default. With -d option, the members of the list will be used in order as delimiters. Enclose comma in double quotes: paste -d "," file1 file2

/usr/xpg4/bin/grep -E 'full regex' filename

The pattern is a full regular expression (this option is only available for some version of grep such as xpg4)

/usr/xpg4/bin/grep -E '(792503|796006|801801)' a_file

Output the rows with at least one of the three numbers

tr 'abc' 'ABC' < a_file.txt

translate
-d delete
tr -d ' ' #deletes spaces
tr -c 'a' '-' everything but 'a'
tr e z
tr '[a-z]' '[A-Z]'
tr ':lower:' ':upper:' tokens, such as :alnum:, :alpha:, :digit:, :blank: (space character), :space: (all whitespace), :punct:
tr '()' '{}'
tr -s '[:blank:]' squeeze out multiple occurences
Note: tr tranlsates character to character. Also see sed

crontab -l

list crontab
mm hh * * d where mm=minutes, hh=hour, d=day in week (0=Sun)
See below for more details on cron configuration

echo $SHELL

See current shell

xhost +
export DISPLAY=ip-add:0.0

Have an x-windows run on another machine

sysconfig -s

System configuration

sysconfig -q vm

Sub-system configuration (here virtual memory)

date +"%m%d %H%M %Y"

Shows date (mon-day hour-minutes year)
%Y year, %m month, %d day, %a day of week, %H hour 00..23, %M minute, %S seconds
%F YYYY-MM-DD, %z time zone, %T HH24:MI:SS, %s seconds since 1970-01-01
Remember the "+" at beginning of format
-u shows GMT
mv a_name.txt a_name`date +"%Y%m%d%H%M"`.txt: rename file with timestamp

date mmddHHMMyyyy

Change the date (default format on Tru64)

date +%s

current epoch time

cal [m] year

Show calendar for year, optionally just a month

bc

Basic calendar. Enter calculation then press ENTER. End with ctrl-D.
Change the number of decimal places with scale = n

grep "19\-OCT\-2004" ...log/listener.log | grep -i genio | grep -v SID

Check for connections to the database on a given date

echo $PATH

Display the $PATH variable

PATH=${PATH}:new_path_to_add

Add a path to $PATH

ls | xargs

Take a multi-line list and make a single-line list

dos2unix in_file_name > out_file_name

Get rid of the CR at the ends of the lines
awk '{ sub("\r$", ""); print }' dos_format > unix_format
sed 's/^M$//' dos_format > unix_format (sed -e option might be needed). Try also tr -d '\r'

unix2dos in_file_name > out_file_name

Change LF into CRLF
awk 'sub("$", "\r")' unix_file > dos_format
sed 's/$'"/`echo \\\r`/" unix_file > dos_format (verify this)

diff file1 file2

Show the differences between two files
-c gives a context of three lines around the changes, -C n gives a context of n lines
-u produces a merged view of the differences
-b ignore blanks
-y side by side (-by is good for side by side of two files)

diff file1 file2

Compare two sorted files. Displays three columns:
rows in file1, rows in file2, rows in both files

diff -rq dir1 dir2

Show the differences between two directories
Option -r shows more details

^S ... ^Q

Stop input and output (remember the screen lock of old days...)

cat a_file | tr '|' '\t'
tr "|" "\t" < cat a_file

Replace pipes with tabs. Remember to pipe in the file or use "<" for file input. The quotes can be simple or double.

sar -u -s 02:00:00

See stored sar results since 2AM

cal 3 2012 | cut -c3-18

One month, Monday to Friday

History

!!

Redo last command (C shell)

!^

First argument of last command (C shell)

!$

Last argument of last command (C shell)

!*

All arguments of last command (C shell)

!-n

Command types n comands ago

history

Show previous commands

set -o vi

Edit the past commands in vi mode. Press escape to edit. Press i to insert a new command.
With this, to see previous command(s): [esc]k (Korn shell)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Keyboard Shortcuts

Ctrl-C Interrupt
Ctrl-Z Suspend
Ctrl-D Exit the bash shell
Ctrl-L Clear the screen
Ctrl-S and Ctrl-Q Stop scrolling and resume output to the screen

Editing line:
Ctrl-A or Home: beginnning of line
Ctrl-E or End: end of line
Ctrl-B Back one character. Alt-B back one word
Ctrl-F Forward one character. Alt-F Forward one word
Ctrl-XX Go to beginning of line, then with Ctrl-XX return to previous position
Ctrl-D Delete Alt-D Delete to end of line
Ctrl-H or backspace
Ctrl-_ (underscore): undo last key press
Ctrl-T Swap the previous two characters

Cut and paste:
Ctrl-W Cut the word before the cursor
Ctrl-K Cut from cursor to end of line
Ctrl-U Cut from beginning of line to cursor
Ctrl-Y Paste what was previously yanked. Note that the clipboard is local to the bash shell.
Ctrl-Ins and Shift-Ins to copy and paste from computer's clipboard
Alt-U Convert to upper case from cursor to end of current word
Alt-L Convert to lower case from cursor to end of current word
Alt-C Convert character under cursor to upper case and go to end of word

History:
Ctrl-P or up arrow: previous command in history
Ctrl-N or down arrow: next command in history
Alt-R Revert changes to command
Ctrl-R Recall: press ctrl-R and type characters (reverse-i-search)
Ctrl-O Run the command found with ctrl-R above
Ctrl-G Exit this recall mode
Tab completion: press tab to complete a directory or file name.
It appears that the shortcuts above require emacs mode (set -o emacs) as opposed to the vi mode (set -o vi)
Many thanks to L.H. at How-To Geek. The website is an excellent source of tips, tricks, and in-depth explanations

Fonts

Location:
- ~/.fonts
- ~/.local/share/fonts
Update with fc-cache command after adding or removing

Formats:
- TrueType (.ttf)
- PostScript Type 1 (.pfb + .pfm)
- OpenType (.otf)

Miscellaneous

Double-click a text to copy, and right-click to paste

curl -O url: Download a file (capital "O")
wget url: Download a file

Cron

Examples:

0 0 * * 0 = weekly
0 0 * * * = daily, at midnight
0 8 * * * = daily, at 08:00
0 * * * * = hourly

# +------------- minute (0 - 59)
# | +------------- hour (0 - 23)
# | | +------------- day of the month (1 - 31)
# | | | +------------- month (1 - 12)
# | | | | +------------- day of the week (0 - 6) (Sunday to Saturday;
# | | | | |                                   7 is also Sunday on some systems)
# | | | | |
# | | | | |
# * * * * * command-to-execute

Terraform Scripts

See working implementation on https://github.com/yekesys/terraform_ec2. It creates a local file and spins up an EC2 instance.

See Module Structure

# comment
// comment
/* multi-line comment */

Basic Commands

Test installation with:
terraform -v

First run after defining Terraform files:
terraform init
This is idempotent, and can be executed multiple times

Show the changes that will be made (like a dry run):
terraform plan

Apply the changes:
terraform apply or
terraform apply -auto-approve

Remove objects with:
terraform destroy

Format the code:
terraform fmt
Check validity:
terraform validate

Download a new version (to be verified):
terraform init -upgrade

Basic structure of a Terraform block:

<BLOCK TYPE> "<BLOCK LABEL>" "<BLOCK LABEL>" {
  # Block body
  <IDENTIFIER> = <EXPRESSION> # Argument
}

State File

The state is stored in the file terraform.tfstate.

Terraform is "declarative". We define the desired end state. Terraform figures out how to get there.
This approach requires that Terraform know the current state. This is in the state file terraform.tfstate (a json file)

Update the state file:
terraform refresh

Use the -refresh-only mode as a safe way to check Terraform state against real infrastructure. It does not update the infrastructure nor the state file:
terraform plan -refresh-only
terraform apply -refresh-only

Best practices for the state file:

• Do NOT update the terraform.tfstate file directly
• The state file should be a shared file
• Implement a locking mechanism on the shared state file
• Back it up, with versioning, e.g. git
• Define a separate state file for each environment (dev, tst, prd)

Show the state from state file:
terraform show

Logging

Log Terraform core:
export TF_LOG_CORE=TRACE
export TF_LOG_PATH=logs.txt
Log a provider:
export TF_LOG_PROVIDER=TRACE
export TF_LOG_PATH=logs.txt
When done, unset the variables:
export TF_LOG_CORE=
export TF_LOG_PROVIDER=

Providers

First, we define the providers

Providers are defined in the root, not in the modules.

Examples of providers: aws, local
Doc for local: https://registry.terraform.io/providers/hashicorp/local/latest/docs
Doc for AWS: https://registry.terraform.io/providers/hashicorp/aws/latest/docs

Provider information should only be in the root module.

Set AWS profile (user) in the main.tf file:

# main.tf

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.16"
    }
  }

  required_version = ">= 1.2.0"
}

provider "aws" { 
  profile = "user2" 
}

Assume a role:

provider "aws" {
  assume_role {
    role_arn = "arn:aws:iam::123456789012:role/dev-full-access"
  } 
}

list of providers:
https://registry.terraform.io/browse/providers
Documentation:
https://registry.terraform.io/providers/hashicorp/aws/latest/docs

Resources

The resource block identifies the type of the resource and name of the resource.
Below is the basic structure of a resource block:
resource "provider_type" "name" {
  ...
}
The resource type is composed of the provider (above provider, which corresponds to the name of the provider) and the type (above type). The name of the resource is my choice (above name).
The id of the resource is provider_type.name (as in the first line of the resource block, with "." between the resource type and the name).

Locks

remote backend:
-lock-timeout=10m : wait 10 minutes for lock to be released

Variables

Define as follows:

variable "var_name" {
  description = "Text ..."
  type        = string  # or bool or number or list(string)
}

Ideally, put all variables in the variables.tf file, although they can be in any file

Get the value with var.var_name in other files.
Inside a string, use "....${var.var_name}..."

Local variables:
locals { var_name = a_value }

Get the value with local.var_name

Define an object:

variable "a-name" {
  type = object({
    name    = string
    address = string
  })
}

Prevent sensitive values from showing in the output. However, nothing prevents these values from showing in the state file, which therefore has to be treated as holding confidential data:

variable "a-name" {
  sensitive = true   # will not show in outputs
}

Outputs

output "a_value" {
  value = aws_instance.example.public_ip
  description = "Text..."
}

Show all outputs with terraform output and a specific variable with terraform output a_value.

For output in json format, do terraform output -json.

Modules

All .tf files in the same directory are part of the same module.
Each module (or directory) should ideally have a README.md file, or README
And should always contain main.tf, variables.tf, outputs.tf, even if empty

Some people say to not use the file names main.tf, variable.tf, outputs.tf in all the modules, but use different file names. Likewise, some people suggest using json files instead of the tfvars format, and calling the files name.tfvars.json instead of name.tfvars. Instead of outputs, use data blocks and tags.

Child modules should not have a provider block. Provider configurations should only be in the root module. If they are in child modules, there can only be one. But requirements for providers can exist in the various modules in "required_providers" block

Example:

# main.tf in root
provider "aws" {
  region = "us-east-1"
}
module "abc" {
  source = "../../abc_module"    # For local sub-directory, use "./sub-dir" notation
  var_name = "asdfasdf"
}

The name "abc" above is the local name that the calling module uses to designate the instance of the module. The source is mandatory.

Multiple module blocks can use the same source. This creates multiple copies, usually with different variables.

All configuration values should be in the variable.tf file

If a variable is used but does not have a value, provide the value at run-time:
terraform apply -var "server_port=8080"
Or:
export TF_VAR_server_port=8080

Catch the output variable values with:
module.the-module-name.the-output-name
Note: the-module-name is not the sub-directory name, but what follows the keyword module in the calling module. The output name is the output defined in the called module.

Loops

Count:

Create three things that are the same:

resource "..." "example" {
  count = 3
  name  = "something${count.index}"
}

This creates something1, something2, and something3

List:

Define the variable as type "list(string)"

variable "var_name" {
  description = "Text ..."
  type        = list(string)
}

In the resource creation:

  count = length(var.var_name)
  filename = var.var_name[count.index]

Get the values with [*]:

output "all_..." {
  value       = aws_iam_user.example[*].arn
  description = "..."
}

Collection:

Define the variable as type "list(string)"

variable "var_name" {
  description = "Text ..."
  type        = list(string)
}

In the resource creation:

  for_each = toset(var.var_name)
  filename = each.value

Get the values with [*]: output "all_..." { value = aws_iam_user.example[*].arn description = "..." }

Module Structure

terraform {
  required_providers {
    providername = {
      source = "hashicorp/providername"
    }
  }
}

provider "providername" {
    version = "~> 1.4"
}

 
module "the_module_name" {
  source       = "./the_module"
  variable1 = "A text"
  variable2 = "filea.txt"
}

 



variable "variable1" {
  description = "...."
}

variable "variable2" {
  description = "...."
  default     = "t2.micro"    # 'default' not 'value'
}

resource "providername_resourcetype1" "the_resource1_name" {
  param1 = var.variable1
}

resource "providername_resourcetype2" "the_resource2_name" {
  param1 = var.variable1
  param2 = var.variable2
  param3 = providername_resourcetype1.the_resource1_name.property
}

output "public_ip" {
  value       = module.the_module_name.public_ip
  description = "The public IP of the web server"
}

output "module_outputs" {
  value       = module.the_module_name
  description = "All the outputs of module"
} # Shows public_ip, variable1, and any others 

 
output "public_ip" {
  value = providername_resourcetype2.the_resource2_name.public_ip
  description = "Web server public IP"
}

output "variable1" {
  value = var.variable1
  description = "...."
}
<== 

Notes:

• All can go into one file. Group into files for ease of maintenance.
• The names of the files can be anything.
  In root, use main.tf, variable.tf, data.tf, outputs.tf.
  In modules use other names for easier troubleshooting: main_modulename.tf, variable_modulename.tf, data_modulename.tf, outputs_modulename.tf.
  
• See documentation for providernames.
• See documentation for resourcetypes . Choose the provider in the drop-down. Click on links to browse submodules and examples. Also see the bottom of the page.
• See the documentation for required configurations and values
• The other names are arbitrary, meaning the developer's choice:
  • The module names
  • The sub-directory names
  • The variable names, including output variable names
  • The resource names
• See documentation for AWS resources
• If you see module.the_module_name
  look for: module "the_module_name"
• If you see var.variable1
  look for: variable "variable1"
• If you see providername_resourcetype2.the_resource2_name
  look for: resource "providername_resourcetype2" "the_resource2_name"
• If you see data.providername_resourcetype2.the_data_element_name
  look for: data "providername_resourcetype2" "the_data_element_name"

Example: Local File

main.tf in root:

provider "local" {
#  version = "~> 1.4"
}
module "create_a_file" {
  source = "./file_module"
  file_content = "\nA text"
  file_name = "filea.txt"
}
module "create_b_file" {
  source = "./file_module"
  file_content = "\nB text"
  file_name = "fileb.txt"
}

file_module/variable.tf:

variable "file_content" {
  description = "What goes in the file"
  type = string
}
variable "file_name" {
  description = "List of file names"
  type = string
}

file_module/main.tf:

resource "local_file" "a-file" {
  content = var.file_content
  filename = var.file_name
}

Example: Multiple Files (with for_each)

main.tf in root:

provider "local" {
#  version = "~> 1.4"
}
module "create_a_file" {
  source = "./file_module"
  file_content = "\nA text"
  file_names = ["file1.txt", "file2.txt", "file3.txt"]
}
module "create_b_file" {
  source = "./file_module"
  file_content = "\nB text"
  file_names = ["fileb1.txt", "fileb2.txt", "fileb3.txt"]
}

file_module/variable.tf:

variable "file_content" {
  description = "What goes in the file"
  type = string
}
variable "file_names" {
  description = "List of file names"
  type = list(string)
}

file_module/main.tf:

resource "local_file" "a-file" {
  content = var.file_content
  for_each = toset(var.file_names)
  filename = each.value
}

Example: AWS Instance

provider "aws" {
  region = "us-east-1"
}

variable "server_port" {
  description = "The port the server will use for HTTP requests"
  type        = number
}


resource "aws_security_group" "instance" {
  name = "terraform-example-instance"
  ingress {
    from_port   = var.server_port
    to_port     = var.server_port
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "example" {
  ami           = "ami-0022f774911c1d690"
  instance_type = "t2.micro"

  # reference to another part of the configuration:
  vpc_security_group_ids = [aws_security_group.instance.id]


  user_data = <<-EOF
              #!/bin/bash
              echo "Hello, World" > index.html
              nohup busybox httpd -f -p "${var.server_port}" &
              EOF

  tags = {
    Name = "terraform-example"
  }

}

output "public_ip" {
  value       = aws_instance.example.public_ip
  description = "The public IP of the web server"
}

output "port" {
  value       = var.server_port
  description = "The port of the web server"
}

Example: S3 Bucket and DynamoDB For Storing tfstate

terraform {
  backend "s3" {
    bucket         = "bucket name"
    key            = "global/s3/terraform.tfstate"
    region         = "us-east-1"
    dynamodb_table = "terraform-up-and-running-locks-table-name"
    encrypt        = true
  }
}

provider "aws" {
  region = "us-east-1"
}


resource "aws_s3_bucket" "terraform_state" {
  bucket = "bucket name"
  versioning { 
    enabled = true 
  } 
  # Enable server-side encryption by default
  server_side_encryption_configuration {
    rule {
      apply_server_side_encryption_by_default {
        sse_algorithm = "AES256"
      }
    }
  }
}


resource "aws_dynamodb_table" "terraform_locks" {
  name         = "terraform-up-and-running-locks-table-name"
  billing_mode = "PAY_PER_REQUEST"
  hash_key     = "LockID"
  # the key has to have "LockID"
  attribute {
    name = "LockID"
    type = "S"
  }
}

output "s3_bucket_arn" {
  value       = aws_s3_bucket.terraform_state.arn
  description = "The ARN of the S3 bucket"
}
output "dynamodb_table_name" {
  value       = aws_dynamodb_table.terraform-up-and-running-locks-table-name.name"
  description = "The name of the DynamoDB table"
}

https://learn.hashicorp.com/collections/terraform/aws-get-started
https://blog.gruntwork.io/an-introduction-to-terraform-f17df9c6d180
https://blog.gruntwork.io/terraform-tips-tricks-loops-if-statements-and-gotchas-f739bbae55f9
Reference

Terragrunt

Keeps Terraform code DRY = Don't Repeat Yourself

Installation Steps:

• Install Terraform
• Install Terragrunt
• Terragrunt configuration in a terragrunt.hcl file

The terragrunt.hcl file contains the following indications:

1. Terraform source
   terraform {source = "tfr:...."} # link to terraform source and version

2. Indicate the AWS region in "generate" block

3. Input values to use for the variables of the module.
   Equivalent to having the contents of the map in a tfvars file and passing that to terraform.

example:

include "root" {
  path = find_in_parent_folders()
}

dependencies {
  paths = ["../vpc", "../mysql", "../redis"]
}

Location:

• command-line option --terragrunt-config
• TERRAGRUNT_CONFIG environment variable
• terragrunt.hcl or terragrunt.hcl.json file in the current working directory

Run terragrunt commands instead of the equivalent terraform commands:

terragrunt plan
terragrunt apply
terragrunt output
terragrunt destroy

key = "${path_relative_to_include()}/terraform.tfstate" # basically the local folder

terragrunt will generate the file:

generate = {
  path      = "backend.tf"
  if_exists = "overwrite_terragrunt"
}

Searches up the directory tree for the root terragrunt.hcl and adds the remote_state configuration from that root:

include "root" {
  path = find_in_parent_folders()
}

https://terragrunt.gruntwork.io/docs/getting-started/quick-start/

Further documentation:

• https://terragrunt.gruntwork.io/
• https://terragrunt.gruntwork.io/docs/
• https://terragrunt.gruntwork.io/docs/getting-started/quick-start/

Plz

The root of repo is defined in: .plzconfig. The .plzconfig file is located in:

• /etc/please/plzconfig
• ~/.config/please/plzconfig
• .plzconfig
• .plzconfig_<arch>
• .plzconfig.local

Profile-specific config file (here "remote")

• .plzconfig.remote
• run with --profile=remote

Sample BUILD file:

python_library(
        name = "my_library",
        srcs = ["file1.py", "file2.py"],
    )

    python_binary(
        name = "my_binary",
        main = "my_main.py",                 # main = entry point
        deps = [":my_library"],
    )

    python_test(
        name = "my_library_test",
        srcs = ["my_library_test.py"],
        deps = [":my_library"],
    )

Do these:

plz build
plz run   # builds and runs
plz test  # build and runs tests

With example above:

plz build //package:my_library
plz build //package:my_binary
plz run //package:my_binary
plz test //package:my_library_test
plz run //package:all      # all targets in the sub-dir package
plz run //package:…      # all targets in sub-dir package and lower

package is the path from the repo root

https://please.build/quickstart.html

Oracle

Set variables

ORACLE_SID=db
export ORACLE_SID

 

mount /dev/disk/cdrom0c /cdrom
ls /cdrom
cd /cdrom/runInstaller

Insert CD and start installer

ssh -l user remote_machine command

Execute command on remote machine. Without command, opens remote shell

uerf -r 300 -R | more

See OS events linked to startup

Some examples:   

sqlplus /nolog <<END_OF_TEXT_LABEL >>a_file
connect / as sysdba;
shutdown immediate;
END_OF_TEXT_LABEL

With the following, the spool_file and the output_file contain the same thing, except when there is an error. The error shows in output_file, but the spool_file is untouched (you may want to delete it explicitely).
sqlplus -s $DB_USER/$DB_PWD@$ORACLE_SID <<END_OF_TEXT_LABEL >>output_file
set pagesize 0 feedback off trimspool on
spool spool_file
select * from ...;
spool off
END_OF_TEXT_LABEL

Get the date:
DATE=`date +"%y%m%d"`

Mail

Local mail

mail

Read mails, if mails exist

mail user-name

Send a mail to a user on the machine. End with "." on empty line.

<enter>

Read next

d

Delete current mail

p

Print current

-

Print previous

q

quit

 

Linux Specifics

Go though this and remove double information

Run a script : ./script_name
echo $ORACLE_SID --> shows value of variable
echo ORACLE_SID --> shows "ORACLE_SID"

srvmgrl --> run the server manager

Set an environment variable
variable_name= value; export variable_name (Bourne shell)
setenv variable_name value (C shell)

Updating the Environment after change of values of environment variables in .profile or .login,
. .profile (Bourne or Korn Shell)
source .cshrc (C shell)

env

obtain or alter environment variables for command execution

set

set the values of all shell variables

setenv

set environment variables

uname [-a]

display name of the current system. -a gives more details.

cat /etc/issue

Shows the distribution

cat /proc/version

Shows the distribution

hostnamectl

Shows the hostname, and also other information including the distribution and kernel version

uname -srm

Shows the kernel version

lshw

Hardware information

lshw | grep product

PC model number

Software Updates

Ubuntu

• sudo add-apt-repository ....
• sudo apt-get update
• sudo apt-get install ....
• sudo apt-get remove ....

Redhat

• up2date -l (-l is command line mode)
• rpm -q a-package-name Is package installed?
• rpm -qa List all packages (grep for what you need)
• rpm -ivh package.name.with.version Install
• rpm -Uvh package.name.with.version Update
• rpm -ev package.name.(no.version) Delete

Ubuntu Notes

USB stick is mounted as /media/SWISSMEMORY with /dev/sda1 (on T30) and with /dev/sdb1 (on DELL)
To mount explicitely:
mkdir /mnt/usb-drive
mount /dev/sda1 /mnt/usb-drive

Define keyboard in menu system > preferences > keyboard. Look for "Switzerland" and expand with the little triangle.

Sudo notes:

• Run all administrative commands with sudo ... or gksudo ... when using a GUI.
• sudo passwd root Defines the root password. Not recommended. The root password is not needed (see next item). If this is used, disable the root account with sudo passwd -dl root (dl is delta lima). See Ubuntu help for more information
• sudo su - or sudo -i: Run as root. Use carefully.
• Add a user with sudo adduser the_user_name sudo

Some links:

• http://www.debianadmin.com/
• Ubuntu Help
• http://www.hypexr.org/bash_tutorial.php
• http://pegasus.rutgers.edu/~elflord/unix/bash-tute.html
• http://tldp.org/LDP/abs/html/index.html Contains not only many examples but is a good reference.
• http://linux.org.mt/article/terminal
• http://www.well.ox.ac.uk/~johnb/comp/unix/ksh.html

FreeNAS

Basics

Installation

Steps

• Use USB drive, or small SSD, with at least 2GB (attached to system board/back of PC)
• Download image from
• Install, and get IP address
• "Embedded" preferred; the configuration is in config.xml file
• On another computer, connect via browser; click "My Account" on left; create admin user
• Create volumes, ZFS preferred, add SMART
• Options: None, Log for ZFS log data, Cache for increasing ZFS performance, Spare for keeping an extra backup disk
• RAID-Z1 preferred if there are three drives of the same size
• Create shares:CIFS preferred
• The read-only option overrides mount point settings
• Option to set browsable, meaning that the share is visible
• Hosts allow option to allow or deny specific hosts
• User access to share: 'valid users = username'; Group access to share: 'valid users = @groupname'