Tutorials

Tutorials - Linux Commands

Linux Help Commands
apropos	Apropos keyword - Show all commands with the keyword in their description. The same as the "man -k" command.
help	Bash shell help for the bash built in command list. The help command gets help for a particular command.
man	Get help from the manual for a command.
man -k	keyword - Show all commands with the keyword in their description
"man 2 kill"	Display page 2 of the kill command
manpath	Determine user's search path for man pages.
info	Documentation on Linux commands and programs similar to the man pages but navigation is organized different.

User and Group Management Commands
Chown	Change the owner of file(s) to another user.
Chroot	Run command or interactive shell with special root directory.
Chsh	Change the login shell.
Adduser	Ex: adduser mark - Effect: Adds a user to the system named mark
Passwd	Set a user's pass word.
Chpasswd	Update password file in batch.
W	Display users logged in and what they are doing.
Wall	Send a message to everybody's terminal.
Who	Display the users logged in.
whoami	Print effective user id.

APT Package Tool
apt-cache search [package]	returns list of packages which corresponds string "searched-packages"
apt-get install [package]	install / upgrade a deb package
apt-get update	update the package list
apt-get upgrade	upgrade all of the installed packages
apt-get remove [package]	remove a deb package from system
apt-get check	verify correct resolution of dependencies
apt-get clean	clean up cache from packages downloaded

Module and kernel management
depmod	Handle loadable modules automatically. Creates a makefile-like dependency file.
dmesg	Print or control the kernel ring buffer. This shows the last kernel startup messages.
genksyms	Generate symbol version information.
insmod	Install loadable kernel module.
lsmod	List currently installed kernel modules.
modprobe	Used to load a set of modules that are marked with a specified tag.
rmmod	Unload loadable modules.

File Management
ls	Directory listing
ls -al	Formatted listing with hidden files
ls -lt	Sorting the Formatted listing by time modification
cd dir	Change directory to dir
cd	Change to home directory
pwd	Show current working directory
mkdir	dir Creating a directory dir
cat >file	Places the standard input into the file
more file	Output the contents of the file
head file	Output the first 10 lines of the file
tail file	Output the last 10 lines of the file
tail -f file	Output the contents of file as it grows, starting with the last 10 lines
touch file	Create or update file
rm file	Deleting the file
rm -r dir	Deleting the directory
rm -f file	Force to remove the file
rm -rf dir	Force to remove the directory dir
cp file1 file2	Copy the contents of file1 to file2
cp -r dir1 dir2	Copy dir1 to dir2;create dir2 if not present
mv file1 file2	Rename or move file1 to file2,if file2 is an existing directory
ln -s file link	Create symbolic link link to file

File Permission
chmod -c –R	chmod file read, write and executable permission
touch -a –t	modify (or create) file timestamp
chown -c –R	change file ownership
chgrp -c –R	change file group permission
touch -a –t	modify (or create) file timestamp

File Compression
bunzip2 file1.bz2	decompress a file called 'file1.bz2'
bzip2 file1	compress a file called 'file1'
gunzip file1.gz	decompress a file called 'file1.gz'
rar a file1.rar test_file	create an archive rar called 'file1.rar'
rar a file1.rar file1 file2 dir1	compress 'file1', 'file2' and 'dir1' simultaneously
rar x file1.rar	decompress rar archive
tar -cvf archive.tar file1	create a uncompressed tarball
tar -tf archive.tar	show contents of an archive
tar -xvf archive.tar	extract a tarball
tar -xvf archive.tar -C /tmp	extract a tarball into / tmp

File Search
find / -name file1	search file and directory into root filesystem from '/'
find / -user user1	search files and directories belonging to 'user1'
find /home/user1 -name \*.c	search files with '.c' extension within directory '/home/user1'
find /usr/bin -type f -atime +100	search binary files are not used in the last 100 days
find /usr/bin -type f -mtime -10	search files created or changed within 10 days
find / -name *.c -exec chmod 755 '{}' \;	search files with '.c' extension and modify permits
find / -xdev -name \*.c	search files with '.c' extension ignoring removable partitions as cdrom, pen-drive, etc.…
locate \*.ps	find files with the '.ps' extension - first run 'updatedb' cmd
whereis halt	show location of a binary file, source or man
which halt	show full path to a binary / executable

Directories
cd /home	enter to directory '/ home'
cd ..	go back one level
cd ../..	go back two levels
cd	go to home directory
cd ~user1	go to home directory
cd -	go to previous directory
mkdir dir1	create a directory called 'dir1'
mkdir dir1 dir2	create two directories simultaneously
mkdir -p /tmp/dir1/dir2	create a directory tree
mv dir1 new_dir	rename / move a file or directory
pwd	show the path of work directory
rm -f file1	delete file called 'file1'
rm -rf dir1	remove a directory called 'dir1' and contents recursively
rm -rf dir1 dir2	remove two directories and their contents recursively
rmdir dir1	delete directory called 'dir1'

Memory Related Commands
free -m	Display the size of memory in MB
free -b	display the size of memory in Bytes.
free -s 5	Update the command for every 5 sec
free –V	The -V option, display free command version information.
Ipcs – m	shared memory on a linux system
Ipcs – a	Shared memory with all details
Memstat -p	To identify how much virtual memory is used by the process' associated
/proc/meminfo	To check memory usage is to read the /proc/meminfo file
Vmstat - s	Memory usage statistics much like the proc command.

Disk Related Commands
Fdisk -l	View all Disk Partitions in Linux (fdisk means fixed disk or format disk)
Fdisk -l /dev/sda	View Specific partitions
Fdisk /dev/sda	Check all available fdisk commands
fdisk –s /dev/sda2	Check the size of specific partitions
mkfs.ext4 /dev/sda4	Format the partitions.
dpkg-query –W	show the used space by installed deb packages
du -sh dir1	estimate space used by directory 'dir1'
du -sk * \| sort -rn	show size of the files and directories sorted by size

Swamp Memory
mkswap /dev/hda3	create a swap filesystem .
swapon /dev/hda3	activating a new swap partitions
swapon /dev/hda2 /dev/hdb3	activate two swap partitions

System Information
arch	Print machine architecture.
df	Shows disk free space.
du	Shows disk usage.
free	Display used and free memory on the system.
lsdev	Display information about installed hardware via files in the /proc directory.
lsof	List open files.
lspci	List PCI devices .
procinfo	Display system status gathered from proc.
pstree	Display a tree of processes.
strace	Trace ssytem calls and signals for a binary program.
stty	Change and print terminal line settings.
uname	Print system information, Prints Linux.
vmstat	Report virtual memory statistics.

Environment
env	Show all environment variables.
export	Set the value of a variable so it is visible to all subprocesses that belong to the current shell.
printenv	Print all or part of environment.
reset	Restores runtime parameters for session to default values.
set	Shows how the environment is set up. This is a builtin bash command.