Linux Shell Basics
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This document provides an overview of GNU/Linux and Bash basics, including their history, file system structure, users and permissions, processes, and Bash functionality. It covers topics such as files and directories, links, file types, locations in the file system, users and groups, process states and signals, the Bash command line interface versus scripts, variables, file streams and pipelines, text processing utilities, program execution and process management, file system management, permissions, and basic network tasks. The document is intended to introduce users to fundamental Linux and Bash concepts.
![POSIX command line arguments
15 of 24
An option is a hyphen followed by a single character, e.g. -o
An option may require an argument, e.g.
-o argument or -oargument
Options that do not require arguments can be grouped, e.g.
-lst is equivalent to -t -l -s
Options can appear in any order, e.g. -lst is equivalent to -tls
Options can appear multiple times.
Options precede other nonoption arguments: -lst nonoption
The -- argument terminates options
grep -RE '^s*<([a-z]+)>.*$' /usr -i --line-number](https://image.slidesharecdn.com/nosovskylinuxshellbasics-140902022043-phpapp01/85/Linux-Shell-Basics-15-320.jpg)
Linux Shell Basics
- 1. GNU/Linux and Bash basics Constantine Nosovsky 1
- 2. Table of contents History. What Linux and Bash are and what they are not File system (structure, files/dirs, links, file types, locations) Users, groups, permissions Processes (organization, types, states, signals) Bash functionality GNU utilities and tools 2 of 24
- 3. Bash and Utilities User session, bash configuration Bash CLI vs. scripts Command execution, POSIX arguments Variables (usage, environment) File streams, pipelines, command substitution Text processing Program execution, processes File system management Permissions Network 3 of 24
- 4. History 4 of 24 1969 – Unix: multi-tasking, multi-user OS in assembly language 1973 – Unix was rewritten to C 1983 – GNU: GNU’s Not Unix. GPL. GCC. GRUB. Bash 1987 – MINIX: educational OS 1991 – Linux kernel. “I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu)” 1993 – Slackware Linux: the first official distribution
- 5. Linux history today 5 of 24 15M lines of code (excluding comments, blanks) // ohloh.net Around 5k commits per month // ohloh.net Some contributor companies: Red Hat, Intel, IBM, Nokia, Samsung, Oracle, Google, AMD, Microsoft // linuxfoundation.org 75% of all kernel development is done by developers who are being paid for their work // linuxfoundation.org Hundreds of distributions, variety of platforms 469 of 500 TOP computers use Linux // top500.org
- 6. File system (structure, files/dirs) Root directory “/” is required to be mounted Every directory contains link to itself “.” and parent directory “..” “~” is a user’s home directory Refer to the file by its Absolute path – starting from the root directory: /bin/bash Relative path: ~/.bashrc, ./hello.sh, ../hello.sh File is a sequence of bytes. Directories contain file metadata: length, timestamps, type, owner, permissions, etc. 6 of 24
- 7. File system (links) Symbolic (soft) link (ln -s) Dir1 File1 metadata File2 metadata … File1 content on disk Hard link (ln) Dir2 File3 metadata File4 metadata … File3 content on disk File1 content on disk Dir1 File1 metadata File2 metadata … Dir2 File1 metadata File3 metadata … 7 of 24
- 8. File system (file types, pseudo fs) Regular file (text, binary), directory, symbolic link, socket, pipe /dev – Devices related files Block, character devices (storage, sound, input, net, tty) Pseudo files (urandom, null) /proc – Processes related files /proc/<PID>/ - information related to the process with PID cpuinfo, meminfo, version, modules, uptime, etc 8 of 24
- 9. File system (some locations) 9 of 24 /boot – loader, kernel images /bin – base programs (shell, system-utils), /sbin – for super user /etc – system configuration, service management scripts /home – home directories of regular users /lib, /lib64 – basic system shared libraries /tmp – temporary file system (cleaned after reboot) /media, /mnt – mounted storage devices /lost+found – used for recovery /var – often changed files: logs, cache, locks /usr – user space software related: executables, libs, docs, src, headers, resources
- 10. Users, groups, permissions 10 of 24 /etc/passwd,group,shadow – user, group, passwords storage File permissions: read, write, execute Dir perm: read(metadata), write(metadata), execute(change dir) Each file has user and group owners Rules applied in order user-group-others (e.g. rwx r-x r--) root (UID=0) has all permissions SUID/GUID – bits to run as user/group owner Sticky bit is used to grand permissions exclusively to the owner Default permissions are set up with umask or mounting fs
- 11. Processes (organization, types) Organization Each process has PID and parent PID (PPID) Each process belongs to a process group Groups are associated with a terminal session Types 11 of 24 System processes are run from kernel in a special way (e.g. init) Daemon – process detached from the session attached Regular user space processes
- 12. Processes (states, signals) Process states (ps) R - Running or runnable (on run queue) D - Uninterruptible sleep (usually IO) S - Interruptible sleep (waiting for an event to complete) T - Stopped, either by a job control signal or because it is being traced Z - Zombie process, terminated but not reaped by its parent Signals (kill) KILL, TERM, STOP, CONT, CHLD 12 of 24
- 13. User session, bash configuration Terminal session is created /bin/login is run for authentication User data are read from /etc/passwd, group (home dir, shell) Specified shell is run for user (parent process of the session) Shell is set up with global settings /etc/bashrc, /etc/profile Shell is set up with user configuration ~/.bashrc, ~/.bash_profile Do your stuff… Exiting from shell will end up terminal session 13 of 24
- 14. Bash CLI vs. scripts Execute script #! /bin/bash command1 command2 ... $ ./script.sh Run commands $ command1 $ command2 $ … Interpret script command1 command2 ... $ bash ./script.sh 14 of 24
- 15. POSIX command line arguments 15 of 24 An option is a hyphen followed by a single character, e.g. -o An option may require an argument, e.g. -o argument or -oargument Options that do not require arguments can be grouped, e.g. -lst is equivalent to -t -l -s Options can appear in any order, e.g. -lst is equivalent to -tls Options can appear multiple times. Options precede other nonoption arguments: -lst nonoption The -- argument terminates options grep -RE '^s*<([a-z]+)>.*$' /usr -i --line-number
- 16. Variables (usage, environment) Usage VAR=value – declaration (script scope) $VAR – access value export VAR – accessible outside the script (session scope) Command line arguments may be accessed like $0, $1,… Environment variables SHELL, USER, HOME, PATH, PWD Use env to list all variables and their values 16 of 24
- 17. File streams, pipelines, command substitution File streams >, >>, < echo ‘hello, world!’ > file grep hello < file find –name file 2>/dev/null 1>find_result find –name file 2>&1 Pipelines stream output of one command to the input of another ps aux | grep ^gptest | tr -s ' ' | cut -f2 -d ' ' | xargs Command substitution echo Current time is `date` 17 of 24
- 18. Text processing Use less to view/navigate the large text files Count symbols, words, lines with wc Print file(s) with cat file1 file2 file3 Use cut to filter columns out, e.g. cut –f5 –d ‘:’ Use grep to match text by pattern Use simple text editor nano for interactive file editing Use tr and sed for stream editing, e.g. sed s/regexp/replacement/ file > file_modified Use head/tail for specific line range, e.g. head –n 10000 dev.log | tail –n 100 18 of 24
- 19. Program execution, process management 19 of 24 Use & to run program in background Use Ctrl+Z to pause the execution in foreground Use bg/fg to continue execution Use Ctrl+C to kill program in foreground Use disown to detach background program from current session. Or run programs in a way nohup <executable> & List processes with ps, top, htop Send signal to process with kill <signal> <pid> Run commands as different user using sudo
- 20. File system management 20 of 24 Mount volumes to file system like mount /dev/sda1 /mnt/d, mount -o loop file.iso /mnt/cdrom Get volume/file(dir) size with df –h / du -sh dir Create new directories with mkdir Change current directory using cd Print current directory using pwd List directories and access file metadata with ls Use find to locate files by name, type, size, timestamps, etc Copy files with cp , move/rename with mv, remove with rm Create links with ln and soft links with ln -s
- 21. Permissions management 21 of 24 Set file permissions with chmod, e.g. chmod o+rw dir -R Change file user/group owner with chown/chgrp Set default permission mask with umask Get your identity with id Use ls –l to read file permissions, e.g. ls -l file -rw-r--r-- 1 root root 30608 Nov 26 2010 file Use su, sudo to run as user Know your limits: mounting options (/etc/fstab), file types
- 22. Network Check server availability with ping, traceroute Get your network configuration with ifconfig, netstat Use download utilities wget, scp You do even have a text browser links 22 of 24
- 23. Learn stuff 23 of 24 Use man <cmd> and <cmd> --help to read documentation Some commands are just obvious: sort, uniq, date Google command line solutions for common problems “How to capture screen in bash” ffmpeg -f x11grab -r 25 -s 800x600 -i :0.0 f.mpg
- 24. Thanks for you attention Questions? 24 of 24