Introduction to Linux Commands
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).
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.
Architecture
File System
root (/)
bin
usr
etc
dev
home
var
tmp
spool
(users’ accounts)
mail
(users’ mail)
bin
log
X11R6
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
Network Commands
• telnet
• ssh
• ftp
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.
ssh
• Secure Shell
• ssh {IP or Computer Name} [username]
• Example
• ssh mrb.bio.fsu.edu merchant
ftp
• File Transfer Protocol
Syntax:
ftp [options] {IP or Hostname}
Example:
ftp 127.0.0.1
Basic Linux Commands
•
•
•
•
•
•
Handling Files and Directories
Text Editors
Compiling and Linking
Handling Processes
Archiving and Compressing Files
Other Useful Commands
Handling Files and Directories
•
•
•
•
•
•
•
•
•
ls
cp
mv
rm
mkdir
cd
rmdir
pwd
chmod
: list files
: copy files
: move files
: remove files
: make directories
: change directories
: remove directories
: print working directory
: change permission mode
ls
• Syntax
– ls [-Options] [name ...]
• Description
– Lists contents of directory.
• Frequently Used Options
–
–
–
–
-a
-d
-l
-F
• Examples
– ls -alF
List all entries, including . and ..
Do not list contents of directories
Long listing
Mark directories with a '/', etc.
cp
• Syntax
– cp [-Options] file1 [file2 ...] target
• Description
– File1 is copied to target.
• Frequently Used Options
– -f
– -i
– -r
Force remove existing file
Ask before removing existing file
Copy directory trees
• Examples
– cp p1.c p2.c
– cp p1.c p2.c mydir
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
rm
• Syntax
– rm [-f] [-i] file . . .
– rm -r [-f] [-i] dirname . . . [file . . .]
• Description
– Removes files or directories.
• Frequently Used Options
– -f
– -i
– -r
• Examples
Removal of files without prompting the user
Interactive removal
Recursive removal
– rm -f p*.o
– rm -r mydir
mkdir
• Syntax
– mkdir [-m mode] [-p] dirname . . .
• Description
– Creates the specified directories.
• Options
– -m
– -p
Specifies the mode to be used
Create missing intermediate directories
• Examples
– mkdir -m 700 letter
– mkdir abc
– mkdir -p ./abc/def/ghi
rmdir
• Syntax
– rmdir [-p] [-s] dirname . . .
• Description
– Removes directories.
• Options
– -p
– -s
Remove the directory dirname and its parent
directories which become empty.
Suppress the message when –p is in effect
• Examples
– rmdir letter
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 ..
pwd
• Syntax
– pwd
• Description
– Prints the path name of the working (current)
directory.
• Examples
– pwd
chmod
•
•
•
Syntax
– chmod [-R] mode file ...
– chmod [-R] [ugoa]{+|-|=}[rwxXstl] file ...
Description
– Changes the permissions mode of a file or directory.
Examples
chmod 400 file - Read by owner
chmod 040 file - Read by group
chmod 004 file - Read by world
chmod 200 file - Write by owner
chmod 020 file - Write by group
chmod 002 file - Write by world
chmod 100 file - execute by owner
chmod 010 file - execute by group
chmod 001 file - execute by world
•
To combine these, just add the numbers together:
chmod 444 file - Allow read permission to owner and group and world
chmod 777 file - Allow everyone to read, write, and execute file
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
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 A i I 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
Compiling and Linking
• cc
- C compiler
- Default behavior is ANSI/ISO C
• make
- Allows programmer to maintain, update,
and regenerate groups of computer programs.
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
– -03
Produce an object file
Invoke optimizer
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
Handling Processes
• ps
: Prints information about active
processes
• kill : Sends a signal to a process
ps
• Syntax
– ps [-Options]
• Description
– Prints information about active processes.
• Frequently Used Options
–
–
–
–
-A
-e
-f
-l
Every process now running
Same as -A
Full listing
Long listing
• Examples
– ps -ef
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
Archiving and Compressing
• tar
• gzip
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
– x
– t
Create
Extract from the tape
List files on the tape
tar
• Frequently Used Modifiers
–v
–f
Verbose
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 -xvwf file.tar
Other Useful Commands
• grep: search files for a pattern
• man : on-line reference manuals
• wc : word, line and byte or character count
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
– -l
– -n
Case-insensitive search
Write file names only
Display line number
• Examples
– grep -i unix p1.c
– grep -n UNIX *.c *.h
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
wc
• Syntax
– wc [ -c|-m ] [ -lw ] [ file . . . ]
• Description
– Counts lines, words, and characters
• Options
–
–
–
–
-c
-m
-l
-w
• Examples
Count
Count
Count
Count
– wc -l *.h *.c
the number of bytes
the number of characters
the number of newline characters
the number of words