The Linux Basics Tutorial provides the basic concepts of Linux. Linux is a family of free open-source operating systems based on the Linux kernel. Linux-based operating systems are known as Linux distributions or distros. Examples include Debian, Ubuntu, Fedora, CentOS, Gentoo, and ArchLinux.

You must use a shell to run the Linux operating system. This is the interface for accessing operating system services. Most Linux distributions use a graphical user interface (GUI) as the shell, primarily to provide user-friendliness. It is common to use them when managing VPS. However, we recommend that you use a more powerful and effective command-line interface (CLI). Tasks that require a multi-step process via the GUI can be completed in seconds by entering commands in the CLI.

However, the structure of the Linux file system is different from Windows and macOS, so it can be a bit difficult for Linux beginners to get started. In addition, Linux-based operating systems rely heavily on command-line interface operations, while most PCs rely on graphical interfaces.
This guide outlines the main command line concepts and features and prepares beginners to learn more about Linux.

Introduction to Linux Basics

Unix variants

• Unix, GNU/Linux, Solaris, IRIX, HP-UX, FreeBSD, OpenBSD, NetBSD, Darwin (Mac), and more…

GNU/Linux distributions

• Ubuntu, Edubuntu, Debian, RedHat, Fedora, Slackware, SuSE, Darwin, and more…
• Family tree of the GNU/Linux distributions

Getting Started

Virtual Consoles

• In Red Hat: available through CTRL+ALT+F[1-6]
• If X is running, it is available as CTRL+ALT+F7

Comment to Changing password

• passwd

Logging-In

• From Mac or LINUX

• From Windows: Open Putty and select ssh.
• Use WinSCP software for file exchange.

Date and Time Commands

• date
  • u display date and time in UTC
  • R display date and time in RFC822 (used in email messages)
• chrony package maintains time by connecting to servers over the Internet.
• cal output a calendar for the current month
  • y print calendar of the current year

Making Arithmetic Calculations

• bc
• supported operators: + – * / % ^ sqrt()

Generating Sequential Numbers

• seq
  • w make all generated numbers of the same width
  • s ‘b’ make b character as the separator between numbers

Getting Help

• man
• info
• apropos search for only exact matches
• whatis to list a one−line description of a program
• Software packages may store their help files in /usr/share/doc
• Online help: SuperMan Pages, Linux Documentation Project (LDP)
• LinuxQuestions.org

Handy shortcuts

Managing Files and Directories

Files and Directories Commands

• pwd
• cd
• ls (see the options in the example below)
• File types that may be listed by ls –l :
  • – regular file
  • d directory
  • l symbolic link
  • b block special file
  • c character special file
  • p named pipe
  • s socket
• cp # for copying between hosts, see next section
• rm
• mv
• mkdir
• rmdir
• touch create empty files or update file timestamps
• File Name Expansion characters can be used with these commands.

Determining File Content

• file

Viewing Files

• cat
• less
• less navigation commands:
  • space ahead one full screen
  • ENTER ahead one line
  • b back one full screen
  • k back one line
  • g top of the file
  • G bottom of the file
  • /text search forward for text (Regular Expressions can be used)
  • n repeat last search
  • N repeat backward last search
  • q quit

Hard and Symbolic (Soft) Links

• ln
• ls –l in case of soft link, it displays the link name and the referenced file

Checking Free Space

• df space usage by file systems
• du disk space with directories and subdirectories

Searching Files By Names

• locate [options] name(s)
• slocate [options] name(s)
• Only the files you own are searched
• Some options are shown in the example below.
• locate.db or slocate.db databases are used
• updatedb or locate -u to manually update the database

Searching Files By Names and Attributes

find [conditions] [–exec cmd {} \;]

• -atime n File was last accessed n days ago
• -ctime n File was last changed n days ago
• -user name File is owned by the user uname (or user ID)
• -group gname File belongs to group gname (or group ID)
• -size n[cwbkMG] b 512-byte blocks (default), c in bytes, w two-byte words, k kilobyte
• -iname case -insensitive version of –name
• -o logical operator between criteria (by default it is AND)
• -not negate (logical NOT)
• -perm mode permission bits are exactly mode (octal or symbolic).
• -perm -mode ALL of the permission bits modes are set for the file.
• -perm +mode Any of the permission bits modes are set for the file.
• -regex pattern Full path filename (not only filename) matches regular expression pattern.
• -mtime n Files was last modified Exactly n24 hours ago.
• -mtime +n Files was last modified >= n24 hours ago.
• -mtime -n Files was last modified <= n*24 hours ago.
• -mmin n Files was last modified n minutes ago.
• −daystart measures time in the options above from the beginning of the current day instead of 24 hours ago.
• -newer Files newer than the modification date

find . –name "*.html"
find -iname snow.png
find -user peter -group peter
find -user joe -not -group joe
find -user joe -o -user jane
find -not \( -user joe -o -user jane \)
find -perm 755 # matches if mode is exactly 755
find -perm +222 # matches if anyone can write
find -perm -222 # matches if everyone can write
find -perm -002 # matches if other can write
find -size 1024k # excatly 1 MB
find -size +1024k # over 1 MB
find -size -1024k # less than 1 MB
find ~ −empty # find empty regular files or directories
find -size +102400k -ok gzip {} \; # OK prompte before acting
find . -regex '.*[124].*ms$'
find ~ −mtime 1 # files modified exactly 24 hours ago
find ~ −mtime 1 −daystart # modified yesterday
find ~ −mtime +356 # one year or longer ago
find ~ −mtime 2 −mtime −4 −daystart # two to four days ago
# files that were modified after May 4 of the current year
touch −t 05040000 /tmp/timestamp
find ~ −newer /tmp/timestamp

Archiving Files

• tar cvf archive_name files … to create an archive file
  • c create a new archived
  • v produces verbose messages
  • f archive file name
  • j use bzip2 compression
  • z use gzip compression
• tar tf archive_name to inspect files in an archive, if the v option is used, the long file list
• tar xvf archive_name to extract an archive file (always to the current directory)

Compression Utilities

• gzip –v file(s) v option displays compression percentage, original file replace only regular files are compressed
• bzip2 –v file better compression
• gunzip filename.gz uncompress the file
• gzip –d filename.gz uncompress the file
• gunzip –c filename.gz list contents of the compressed file in STDOUT, the file unchanged
• bunzip2 –v file

Text File Processing Tools

• Check the section Text File Processing Tools

Users, Groups, and Permissions

Change Password

• passwd

Change Your Identity

• su username
• su – username # start a login shell

User Information Commands

• whoami # who you are
• groups, id # what groups you belong to
• users, who, w # who is logged on
• last # login/reboot history

Changing File Ownership

• chown user_name file|directory
• chgrp group_name file|directory

Changing Permissions

• chmod mode file
  • where mode is: [u,g or o] [+ or -] [r, w or x] (Symbolic Method)
  • where mode is: 4:r 2:w 1:x (Numeric Method)

Default File Permission

• umask # if the case of 0002, 664 permission for files, 775 for directories

Special Permission

• chmod Xnnn # X: 4 for suid, 2 for sgid, 1 for sticky bit
• suid and sgid affect executables files: the program runs with the owner, not the executor.
• sgid and sticky bits affect directories:
  • Sticky bit: Files in a directory can be deleted individually by the owner or root directory writes permission.
  • Sgid: Files created in the directory inherit group membership from the directory, Not the user.

bash Shell Basics

File Blobbing

• matches zero of more characters
• ? matches any single character
• [a-z] matches a range of characters
• [^a-z] matches all except the range

History Tricks

• History
• Use the up and down keys to scroll through the previous command.
• To find the command in the command history, type ctrl -r.
• Command Esc + will Get the last argument from the previous command.
• ! n will re-execute command number n

Command Line Expansion

• Command Expansion: $() or “
• Brace Expansion: { }
• Arithmetic: $[]
• Arithmetic Evaluations: + – * / ** % (Full list in Arithmetic Evaluation section in bash man page)
• \ backslash makes the next character literal and can be used as the last character on a line to continue the command on the next line.
• To pass special characters as a string: $’string’
• Special backslash escape sequences:
  • \a Alert (rings the system bell).
  • \b Backspace.
  • \e Escape.
  • \f Form feed.
  • \n Newline.
  • \r Carriage return.
  • \t Horizontal tab.
  • \v Vertical tab.
  • \ Backslash.
  • \NNN Character whose ASCII code is NNN in octal (base 8).
• Filename Expansion Characters: used with commands handling files and directories:
  • zero or more characters
  • ? exactly one character
  • [list] one character in the list. Examples: [abc],[a-m], a[-b]c
  • [!list] except the characters in the list. For example, a[!b]c matches aac a-c adc, but
  • not abc.

Local Shell Variables

• VARIABLE=value
• echo $VARIABLE
• To see a list of the local variables that configure the shell, see the Shell Variables section of the bash man page.
• Common Local Configuration Variables
  • PS1 the prompt
  • \d date
  • \h short hostname
  • \t time
  • \u user name
  • \w current working directory
  • ! history number of the current command
  • \$ $ for superusers, # for non-privileged user
  • HISTFILESIZE how many commands to save in the history
  • COLUMNS width of the terminal
  • LINES height of the terminal
• Common Local Information Variables
  • HOME user’s home directory
  • EUID user’s effective UID

Aliases

• alias

Type

• type to ask the shell what it is using to fulfill the command

Environment Variables

• export VARIABLE=value
• Common Environment Variables:
  • HOME user home directory path
  • LANG default language (like en_US.UTF-8)
  • PWD current working directory
  • EDITOR default editor used by programs
  • LESS options to pass to the less command
• reset when the screen becomes corrupted

Showing Path of Executable

• which

Login and Non-Login Shells

• Login shells are:
  • Any shell created at login (includes X login)
  • su –
• non-login shells are:
  • su
  • graphical terminals
  • executed scripts
  • any other bash instances

Startup and Logout Scripts

Login Sells

Non-Login Shells

Logout Script

Recording a Shell Session

• Script record session file name typo entry
• End session Stop recording

Standard I/O and Pipes

Redirecting Output to a File

• Redirect STDOUT to file (overwrite)
• >> Redirect STDOUT to file (append)
• 2> Redirect STDERR to file
• &> Redirect all output to file
• 2>&1: Redirects STDERR to STDOUT
• (): Combines STDOUTs of multiple programs

Redirecting STDOUT to a Program (Piping)

Pipes (the | character) can connect commands

Redirecting to Multiple Targets

• tee – read from standard input and write to standard output and files
• command1 | tee filename | command2 store STDOUT of command1 in the filename, then pipes to command2

Redirecting STDIN from a File

Redirect standard input with <

Sending Multiple Lines to STDIN

• Redirect multiple lines from keyboard to STDIN with <<WORD
• All text until WORD is sent to STDIN

Text Files and String Manipulation

Viewing File Contents

• cat dump one or more files to STDOUT
• less view file or STDIN one page at a time
• fewer navigation commands:
  • space ahead one full screen
  • ENTER ahead one line
  • b back one full screen
  • k back one line
  • g top of the file
  • G bottom of the file
  • /text search forward for text
  • n repeat last search
  • N repeat backward last search
  • q quit

Viewing File Excerpts

• head
• tail

Extracting Text by Column

• cut
  • -d to specify the column delimiter (default is TAB)
  • -f to specify the column to print
  • -c to cut by characters

Gathering Text Statistics

• wc
  • -l for only line count
  • -w for only word count
  • -c for only byte count
  • -m for character count

Sorting Text

• sort
  • -r performs a reverse (descending) sort
  • -n performs a numeric sort
  • -f ignores (folds) case of characters in strings
  • -u (unique) removes duplicate lines in the output
  • -t c uses c as a field separator
  • -k X sorts by c-delimited field X

Eliminating Duplicates

• sort -u: removes duplicate lines from the input
• uniq: removes duplicate adjacent lines
  • -c prefix lines by the number of occurrences
  • -d only print duplicate lines
  • -u only print unique lines

Comparing Files

• diff

Spell Checking with aspell

• aspell

Converting Characters

• tr converts characters in one set to corresponding characters in another set

Combining Files

• paste combines files horizontally and separates the pasted lines by TAB by default.

Expanding Tabs Into Spaces

• expand convert the tabs in the file to spaces

Regular Expressions

Wildcard Characters

• another single character
  • . any single character
  • [abc] any single character in the set
  • [a-c] any single character in the range
  • [^abc] any single character not in the set
  • [^a-c] any single character not in the range

Modifiers

• number of the previous character
  • * zero or more of the previous char
  • \+ one or more of the previous char
  • \? zero or one of the previous char
  • {i} exactly i of the previous char
  • {i,} i or more of the previous char
  • {i,j} i to j of the previous char

Anchors

• match the beginning or end of a line or word
  • ^ line begins with
  • $ line ends with
  • \< word begins with
  • > word ends with

Other expressions

• [:alnum:] Alphanumeric characters 0 to 9 OR A to Z or a to z
• [:alpha:] Alpha character a-z A-Z
• [:cntrl:] Control characters
• [:digit:] Digits 0 to 9
• [:graph:] Graphics characters
• [:print:] Printable characters
• [:punct:] Punctuation ” ‘ ? ! ; : # $ % & ( ) * + – / < > = @ [ ] \ ^ _ { } | ~
• [:space:] White spaces (space, tab, NL, FF, VT, CR)
• [:blank:] Space and Tab characters only

Extended Regular Expressions

• Except for word anchors, basic regular expressions requiring a preceding backslash do not require a backslash
• Used by:
  • egrep
  • grep –E
  • awk

Extracting Text by Keyword

• grep [OPTION]… PATTERN [FILE] …
  • -i to search case-insensitively
  • -n to print line numbers of matches
  • -v to print lines not containing the pattern
  • -AX to include the X lines after each match
  • -BX to include the X lines before each match
• grep uses by default basic Regular Expressions
• egrep uses Extended Regular Expressions

Search and Replace

• sed (stream editor) uses regular expressions in search string (but not in replace)

Editing Text by awk

• awk
• All extended regular expressions work except curly brace counters. To use them, use — posix or –re-interval options.

Using the Text Editor vi

Modes

Command Mode

• The default mode of vim
• Move by the character: Arrow Keys, h, j, k, l
• Move by word: w, b
• Move by sentence: ), (
• Move by paragraph: }, {
• Jump to line x: xG
• Jump to end: G

Insert mode

• i begin to insert mode at the cursor
• A append to the end of the line
• I insert it at beginning of the line
• o insert new a line (below)
• O insert a new line (above

Ex Mode

• :w writes (saves) the file to disk
• :wq writes and quits
• :q! quits, even if changes are lost

Search and Replace (Command Mode)

• /, n, N Search
• <>/<>/<> Search/Replace (as in sed command)

Manipulating Text (Command Mode)

The action followed by Target

Possible actions:

• change (c)
• cut (d)
• yank (y)
• paste (p) without target

Possible target:

• Line as in action
• Letter l
• Word w
• Sentence ahead )
• Sentence behind (
• Paragraph above {
• Paragraph below }

Undoing Changes (Command Mode)

• u Undo the most recent change.
• U Undo all changes to the current line since the cursor landed on the line.
• Ctrl-r redo the last “undone” change

Visual Mode

• Allows selection of blocks of text
• v starts character-oriented highlighting
• V starts line-oriented highlighting
• Highlighted text can be deleted, yanked, changed, filtered, searched/replaced, etc.

Using Multiple “windows”

• Multiple documents can be viewed on a single vim screen.
• Ctrl-w, s splits the screen horizontally
• Ctrl-w, v splits the screen vertically
• Ctrl-w, Arrow moves between windows
• :q close the current window
• Ex-mode instructions always affect the current window

Configuring vi and vim

• :set or :set all Configuring on the fly
• ~/.vimrc or ~/.exrc Configuring permanently
• :set showmode show when you are in insert mode
• :set ic ignore case when searching
• :set noic turn to ignore case off
• :set nu turn on line numbering
• :set nonu turn line numbering off

Managing Processes

Listing Processes

• the top continuously updated list
• ps shows processes from the current terminal by default
  • -a all processes except session leaders and processes not associated with a terminal.
  • -A prints all processes. Identical to -e.
  • -e prints all processes. Identical to -A.
  • -H shows process hierarchy
  • –u prints process owner information
  • –l show log-listing format
  • –L show thread information
  • –a exclude processes not associated with a terminal
  • –x includes processes not attached to terminals
  • –f prints process parentage
  • — sort some sorting options are:
    • c cmd simple name of executable
    • C CPU utilization
    • r RSS resident set size
    • R resident pages
    • s size memory size in kilobytes
    • S share amount of shared pages
    • T start_time time process was started
    • U uid user ID number
    • u user name
    • v vsize total VM size in kB
  • -o CODE prints custom information where CODE took from the following list:

Process statuses:

• R Runnable: executing
• S Sleeping: waiting for an event to occur to wake up
• T Stopped: not executing
• D Uninterruptible sleep
• Z Zombie: just before a process dies. If no notification acknowledgment is received from parent, all resources except PID are released.

When the stat keyword is used, additional characters may be displayed:

• < high-priority (not nice to other users)
• N low-priority (nice to other users)
• L has pages locked into memory (for real-time and custom IO)
• s is a session leader
• l is multi-threaded
• + is in the foreground process group

Sending Signals to Processes

• kill [-signal] pid(s) the default signal is TERM (15)
• kill –l lists the signals (for more info use man 7 signal)

Changing Process Scheduling Priority

• nice [-n adj ] command where adj between -20 (highest) and 19 (lowest)
• renice adj [[-p|-g] PID [[-u] user] for running processes

Listing Background and Suspended Jobs

• jobs

Resuming Suspended Jobs

• bg [%job_number] or Ctl+Z brings the current process into the background
• fg [%job_number] brings the background process into the foreground

You can use the following code example to test the commands:

Compound Commands

• List of commands separated by semi-colons
• Put the list between () to run them all in a subshell (treat it all as one command)

Scheduling a Process

• at time commands entered one per line, terminate with Ctl+D
• atq [user] lists the current at jobs
• atrm [user|atJobID] removes at jobs

Scheduling a Process Periodically

• crontab is used to install, deinstall or list the tables (crontabs).
  • -u user the user whose crontab is to be tweaked
  • -l Display the current crontab file
  • -r Remove the current crontab file
  • -e edit. After exiting from the editor, the modified crontab will be installed
• Cronttab file:
  • Space delimited
  • Fields: minute, hour (0-23), day of the month (0-31), month (1-12), and day of the week (0=Sun to 6).

bash Shell Scripting Basics

Creating Shell Scripts

• First-line contains the magic “shbang” #!/bin/bash
• Comments start with #
• One command spans multiple lines with \
• For convenient, they have sh extension

Handling Input

• read assigns an input word(s) to a shell variable
• words are separated by default with space. IFS variable controls the separator.

Shell Script Debugging

• Modify the shebang as follows
  • !/bin/bash –x
  • !/bin/bash -v

• Alternatively, Invoke the shell interpreter with debug options
  • bash –x scriptname
  • bash –v scriptname

Handling Positional Parameters (Arguments)

• accessed by $1, $2, …, $9, ${10},${11},…
• $0 reserved for the program name
• $* holds all command line parameters
• $# holds number of command line parameters

Using Functions

• functionname() { [return …] }
• Arguments passed to a function are accessed by its positional parameters $1, $2 … etc.
• Does the return keyword set the special variable $?
• Variables are made local in a function using local keyword.

Exit Status

• $? contains exit status of the most recently executed command.
• It takes values 0 for success, 1-255 for failure
• exit sets an exist status in a script

Conditional Execution

• <cmd1> && <cmd2> execute cmd2 if cmd1 succeeds
• <cmd1>|| <cmd2> execute cmd2 if cmd1 fails

Using the if Statement

if [ condition ]; then
…
elif [condition]; the
…
else
…
fi

Using the Case Statement

case variable in
pattern1)
<command>;;
pattern2)
<command>;;
esac

Using the For Loop

for variable in list-of-vlaues
do
commands...
done

Using the While loop

while condition
do
commands...
done

Disrupting Loops

• continue to jump back to the initial condition
• break jump to the command past the done

File Tests

• Common file tests are:
  • -e file exists
  • -f file exists and is a regular file
  • -d file exists and is a directory
  • -x file exists and is an executable
  • -h file exists and is a symbolic link
  • -r file exists and is readable by you
  • -s file exists and is not empty
  • -w file exists and is writable by you
  • -O file exists and is effectively owned by you
  • -G file exists and is effectively owned by your group
• help test for the complete list

String Tests

String operators:

• -z STRING True if the string is empty.
• -n STRING True if the string is not empty.
• STRING1 = STRING2 True if the strings are equal.
• STRING1 != STRING2 True if the strings are not equal.
• STRING1 < STRING2 True if STRING1 sorts before STRING2 lexicographically. STRING1 > STRING2 True if STRING1 sorts after STRING2 lexicographically.

Shell Option Test

Shell option operator

• -o OPTION True if the shell option OPTION is enabled.

Logical Tests

Logical Operators

• ! EXPR True if expr is false.
• EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
• EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.

Comparison

Comparison Operators

• arg1 OP arg2 OP is one of: -eq, -ne, -lt, -le, -gt, or -ge.