Introduction to Linux Commands

1. Introduction to Linux Commands

2. 3 Definitions of Linux • Linux Kernel: The very low-level software that manages your computer hardware and provides a library (POSIX) interface for user-level software. The Linux kernel runs on many platforms (Intel x86 and IA-64, Alpha, MIPS, HP PA-RISC, PowerPC, IBM S/390, SPARC, Motorola 680x0, etc.). • GNU/Linux OS: The Linux kernel plus utility software to provide a useful working environment. • Linux Distributions: The packaging of the Linux Kernel, the GNU/Linux OS and lots of other software to make Linux easy to install, configure, and use (at least for the target audience).

3. Architecture • Kernel: Schedules programs, Manages data/file access and storage, Enforces security, Performs all hardware access. • Init: First program run by kernel on booting. • Shell: Presents each user a prompt, Interprets commands typed by user, Executes users commands, Provides user/programming environment.

4. Architecture

5. root (/) bin usr etc dev var home tmp bin spool log X11R6 (users’ accounts) mail (users’ mail) File System

6. Utilities • Basic Utilities • Directory/File management: cd, ls, pwd, mkdir, rmdir, cp, mv, rm, find, du, file • File viewing/editing: touch, more, less, ed, vi, emacs • User management: passwd, chmod, chown, su, who • Process management: kill, killall, ps • Documentation: man, info, /usr/share/doc • Applications: X11, KDE, Gnome, OpenOffice, Apache, Sendmail, Gimp, Mozilla Firefox • Security Software: gpg, ssh, iptables, ACID, snort, prelude, tcpdump, ethereal, nmap, nessus, tcpspy, tiger, ClamAV, spamassassin

7. Network Commands • telnet • ssh • ftp

8. telnet • Connect to a host machine over the network. • Syntax: telnet [options] {IP or Computer Name} [port number] • Example: telnet 127.0.0.1 telnet 127.0.0.1 25 SMTP may not be running. • Alternative: nc (from the netcat package) • Telnet does not encrypt connections and so is NOT secure. • Use ssh for encrypted secure connections.

9. ssh • Secure Shell • ssh {IP or Computer Name} [username] • Example • ssh mrb.bio.fsu.edu merchant

10. ftp • File Transfer Protocol Syntax: ftp [options] {IP or Hostname} Example: ftp 127.0.0.1

11. Basic Linux Commands • Handling Files and Directories • Text Editors • Compiling and Linking • Handling Processes • Archiving and Compressing Files • Other Useful Commands

12. Handling Files and Directories • ls: list files • cp : copy files • mv : move files • rm : remove files • mkdir: make directories • cd: change directories • rmdir: remove directories • pwd: print working directory • chmod : change permission mode

13. ls • Syntax • ls [-Options] [name ...] • Description • Lists contents of directory. • Frequently Used Options • -a List all entries, including . and .. • -d Do not list contents of directories • -l Long listing • -F Mark directories with a '/', etc. • Examples • ls -alF

14. cp • Syntax • cp [-Options] file1 [file2 ...] target • Description • File1 is copied to target. • Frequently Used Options • -f Force remove existing file • -i Ask before removing existing file • -r Copy directory trees • Examples • cp p1.c p2.c • cp p1.c p2.c mydir

15. mv • Syntax • mv [-Options] file1 [file2 ...] target • Description • File1 is moved to target. • Frequently Used Options • -f Removes existing files without prompting the user • -i Asks before removing existing file • Examples • mv p*.c mydir

16. rm • Syntax • rm [-f] [-i] file . . . • rm -r [-f] [-i] dirname . . . [file . . .] • Description • Removes files or directories. • Frequently Used Options • -f Removal of files without prompting the user • -i Interactive removal • -r Recursive removal • Examples • rm -f p*.o • rm -r mydir

17. mkdir • Syntax • mkdir [-m mode] [-p] dirname . . . • Description • Creates the specified directories. • Options • -m Specifies the mode to be used • -p Create missing intermediate directories • Examples • mkdir -m 700 letter • mkdirabc • mkdir -p ./abc/def/ghi

18. rmdir • Syntax • rmdir [-p] [-s] dirname . . . • Description • Removes directories. • Options • -p Remove the directory dirname and its parent directories which become empty. • -s Suppress the message when –p is in effect • Examples • rmdir letter

19. cd • Syntax • cd [directory] • Description • Change working directory. • If directory is not specified, the value of shell parameter $HOME is used as the new working directory. • Examples • cd • cd ./abc/def/ghi • cd ..

20. pwd • Syntax • pwd • Description • Prints the path name of the working (current) directory. • Examples • pwd

21. chmod • Syntax • chmod [-R] mode file ... • chmod [-R] [ugoa]{+|-|=}[rwxXstl] file ... • Description • Changes the permissions mode of a file or directory. • Exampleschmod 400 file - Read by ownerchmod 040 file - Read by groupchmod 004 file - Read by world chmod 200 file - Write by ownerchmod 020 file - Write by groupchmod 002 file - Write by worldchmod 100 file - execute by ownerchmod 010 file - execute by groupchmod 001 file - execute by world • To combine these, just add the numbers together:chmod 444 file - Allow read permission to owner and group and worldchmod 777 file - Allow everyone to read, write, and execute file

22. Text Editors • pico - Simple, easy-to-use text editor • vi - Text editor based on an underlying line editor ex • emacs - Powerful and extensible - Hard to learn

23. vi • vi Modes: • Command mode : Normal and initial mode. Other modes return to command mode upon completion. ESC(escape) is used to cancel a partial command. • Input mode : Entered by setting any of the following options: a AiI o O c C s S R . Arbitrary text may then be entered. Input mode is normally terminated with ESC character. • Last line mode : Reading input for : / ? or !.Terminates by typing a carriage return

24. Compiling and Linking • cc - C compiler - Default behavior is ANSI/ISO C • make - Allows programmer to maintain, update, and regenerate groups of computer programs.

25. cc / gcc • Syntax • cc [-Options] ... file ... • Description • *.c are assumed to be C source programs. • *.o are compiled object files. • a.out is the default output program name. • Frequently Used Options • -c Produce an object file • -03 Invoke optimizer

26. cc / gcc • -o out Name the final output file out. • -Dname Define the name to the C macro processor • -Idir Seek dir for include files • Examples • cc p1.c

27. Handling Processes • ps : Prints information about active processes • kill : Sends a signal to a process

28. ps • Syntax • ps [-Options] • Description • Prints information about active processes. • Frequently Used Options • -A Every process now running • -e Same as -A • -f Full listing • -l Long listing • Examples • ps -ef

29. kill • Syntax • kill [-signal] pid . . . • kill –l (the letter ‘L’ in lowercase) • Description • Sends a signal to the specified processes. • The value of signal may be numeric or symbolic. • Signal 15 is the default signal. • kill –l lists the defined signals. • Examples • kill 389 • kill –3 401 402 • kill -HUP 99999

30. Archiving and Compressing • tar • gzip

31. tar • A ".tar" file is not a compressed file, it is actually a collection of files within a single file uncompressed. If the file is a .tar.gz ("tarball") or ".tgz" file it is a collection of files that is compressed. • Syntax • tar key [arguments] [name...] • Description • Saves and restores multiple files on a single file. • The key argument controls tar's actions. • Frequently Used Functions • c Create • x Extract from the tape • t List files on the tape

32. tar • Frequently Used Modifiers • v Verbose • f Next argument is the name of the archive • Examples • Creating a tarball: tar -cvwf file.tar myfile1.txt mypic1.jpeg • Extracting from a tarball tar -xvwffile.tar

33. Other Useful Commands • grep: search files for a pattern • man : on-line reference manuals • wc: word, line and byte or character count

34. grep • Syntax • grep [-E| -F] [-c| -l| -q] [-insvx] pattern_list [file . . .] • Description • Searches the input files, selecting lines matching one or more patterns • Frequently Used Options • -i Case-insensitive search • -l Write file names only • -n Display line number • Examples • grep -iunix p1.c • grep -n UNIX *.c *.h

35. man • Syntax • man [-Options] [-M path] [-T macropackage] [ -s section] name ... • man [-M path] -k keyword ... • Description • On-line reference manuals • Frequently Used Sections • 1 User commands and application programs • 2 System calls • 3 Library functions • Examples • man -s 1 mkdir • man mkdir • man -k pipe

36. wc • Syntax • wc [ -c|-m ] [ -lw ] [ file . . . ] • Description • Counts lines, words, and characters • Options • -c Count the number of bytes • -m Count the number of characters • -l Count the number of newline characters • -w Count the number of words • Examples • wc -l *.h *.c