Basic Linux commands.
I often forget commands 
I decided to post them at one place (cheers to websites from which I copied the details ) – now I don’t have to google everytime — I am sorry google you missed few of my hits 
ls
List files/directories in a directory, comparable to dir in windows/dos.
ls -la
Shows all files (including ones that start with a period), directories, and details attributes for each file.
cd
Change directory (e.g cd /usr/local/bin)
cd ~
Go to your home directory
cd -
Go to the last directory you were in
cd ..
Go up a directory
cat
Print file contents to the screen
cat filename.txt
Print the contents of filename.txt to your screen
tail
Similar to cat, but only reads the end of the file
tail /var/log/messages
See the last 20 (by default) lines of /var/log/messages
tail -f /var/log/messages
Watch the file continuously, while it’s being updated
tail -200 /var/log/messages
Print the last 200 lines of the file to the screen
head
Similar to tail, but only reads the top of the file
head /var/log/messages
See the first 20 (by default) lines of /var/log/messages
head -200 /var/log/messages
Print the first 200 lines of the file to the screen
more
Llike cat, but opens the file one screen at a time rather than all at once
more /etc/userdomains
Browse through the userdomains file. hit Spaceto go to the next page, q to quit
less
Page through files
od
View binary files and data
xxd
Also view binary files and data
gv
View Postscript/PDF files
xdvi
View TeX DVI files
nl
Number lines
touch
Create an empty file
touch /home/burst/public_html/404.html
Create an empty file called 404.html in the directory /home/burst/public_html/
file
Attempts to guess what type of file a file is by looking at it’s content.
file *
Prints out a list of all files/directories in a directory
cp
Copy a file
cp filename filename.bak
Copies filename to filename.bak
cp -a /etc/* /root/etc/
Copies all files, retaining permissions form one directory to another.
cp -av * ../newdirectory
Copies all files and directories recurrsively in the current directory INTO newdirectory
mv
Move a file command
mv oldfilename newfilename
Move a file or directory from oldfilename to newfilename
rm
delete a file
rm filename.txt
deletes filename.txt, will more than likely ask if you really want to delete it
rm -f filename.txt
deletes filename.txt, will not ask for confirmation before deleting.
rm -rf tmp/
recursively deletes the directory tmp, and all files in it, including subdirectories.
chmod
changes file access permissions. The set of 3 go in this order from left to right:
USER – GROUP – EVERONE
0 = — No permission
1 = –X Execute only
2 = -W- Write only
3 = -WX Write and execute
4 = R– Read only
5 = R-X Read and execute
6 = RW- Read and write
7 = RWX Read, write and execute
chmod 000
No one can access
chmod 644
Usually for HTML pages
chmod 755
Usually for CGI scripts
chown
Changes file ownership permissions
The set of 2 go in this order from left to right:
USER – GROUP
chown root myfile.txt
Changes the owner of the file to root
chown root.root myfile.txt
Changes the owner and group of the file to root
stat
Display file attributes
grep
Llooks for patterns in files
grep root /etc/passwd
Shows all matches of root in /etc/passwd
grep -v root /etc/passwd
Shows all lines that do not match root
ln
Create’s “links” between files and directories
ln -s /usr/local/apache/conf/httpd.conf /etc/httpd.conf
Now you can edit /etc/httpd.conf rather than the original. changes will affect the orginal, however you can delete the link and it will not delete the original.
wc
Word count
wc -l filename.txt
Tells how many lines are in filename.txt
find
Utility to find files and directories on your server.
find / -name “filename”
Find the file called “filename” on your filesystem starting the search from the root directory “/”.
locate filename
Find the file name and path of which contains the string “filename”. Run ‘updatedb’ to build index.
EDITORS
Most popular editors available on UNIX platforms.
pico
Friendly, easy to use file editor
pico /home/burst/public_html/index.html
Edit the index page for the user’s website.
vi
Popular editor, tons of features, harder to use at first than pico
vi filename.txt
Edit filename.txt. All commands in vi are preceded by pressing the escape key. Each time a different command is to be entered, the escape key needs to be used. Except where indicated, vi is case sensitive. Fore more commands go to: http://www.intellink.net/vi-qref.htm
H — Upper left corner (home)
M — Middle line
L — Lower left corner
h — Back a character
j — Down a line
k — Up a line
^ — Beginning of line
$ — End of line
l — Forward a character
w — Forward one word
b — Back one word
fc — Find c
; — Repeat find (find next c)
:q! — This force quits the file without saving and exits vi
:w — This writes the file to disk, saves it
:wq — This saves the file to disk and exists vi
:LINENUMBER : EG :25 — Takes you to line 25 within the file
:$ — Takes you to the last line of the file
:0 — Takes you to the first line of the file
emacs
Another popular editor. For more commands go to http://www.hsrl.rutgers.edu/ug/emacs_qref.html
C-\ t — Tutorial suggested for new emacs users.
C-x C-c exit emacs
emacs filename.txt
Edit filename.txt. While you’re in emacs, use the following quickies to get around:
C-x C-f — read a file into emacs
C-x C-s — save a file back to disk
C-x i — insert contents of another file into this buffer
C-x C-v — replace this file with the contents of file you want
C-x C-w — write buffer to specified file
C-f — move forward one character
C-b — move backward one character
C-n — move to next line
C-p — move to previous line
C-a — move to beginning of line
C-e — move to end of line
M-f — move forward one word
M-b — move backword one word
C-v — move forward one screen
M-v — move backward one screen
M-< --- go to beginning of file
M-> — go to end of file
NETWORK
Some of the basic networking utilities.
w
Shows who is currently logged in and where they are logged in from.
who
This also shows who is on the server in an shell.
netstat
Shows all current network connections.
netstat -an
Shows all connections to the server, the source and destination ips and ports.
netstat -rn
Shows routing table for all ips bound to the server.
netstat -an |grep :80 |wc -l
Show how many active connections there are to apache (httpd runs on port 80)
top
Shows live system processes in a formatted table, memory information, uptime and other useful info.
While in top, Shift + M to sort by memory usage or Shift + P to sort by CPU usage
top -u root
Show processes running by user root only.
route -n
Shows routing table for all ips bound to the server.
nslookup yahoo.com
Query your default domain name server (DNS) for an Internet name (or IP number) host_to_find.
top
Shows live system processes in a formatted table, memory information, uptime and other useful info.
While in top, Shift + M to sort by memory usage or Shift + P to sort by CPU usage
top -u root
Show processes running by user root only.
route -n
Shows routing table for all ips bound to the server.
nslookup yahoo.com
Query your default domain name server (DNS) for an Internet name (or IP number) host_to_find.
traceroute yahoo.com
Have a look how you messages travel to yahoo.com
ifconfig
Display info on the network interfaces.
ifconfig -a
Display into on all network interfaces on server, active or inactive..
ping
Sends test packets to a specified server to check if it is responding properly
tcpdump
Print all the network traffic going through the network.
arp
Command mostly used for checking existing Ethernet connectivity and IP address
SYSTEM TOOLS
Many of the basic system utilities used to get things done.
ps
ps is short for process status, which is similar to the top command. It’s used to show currently running processes and their PID.
A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).
ps
ps is short for process status, which is similar to the top command. It’s used to show currently running processes and their PID.
A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).
ps U username
Shows processes for a certain user
ps aux
Shows all system processes
ps aux –forest
Shows all system processes like the above but organizes in a hierarchy that’s very useful!
kill
terminate a system process
kill -9 PID
Immediately kill process ID
killall program_name
Kill program(s) by name. For example to kill instances of httpd, do ‘killall httpd’
du
Shows disk usage.
du -sh
Shows a summary of total disk space used in the current directory, including subdirectories.
du / -bh | more
Print detailed disk usage for each subdirectory starting at the “/”.
last
Shows who logged in and when
last -20
Shows only the last 20 logins
last -20 -a
Shows last 20 logins, with the hostname in the last field
pwd
Print working directory, i.e., display the name of my current directory on the screen.
hostname
Print the name of the local host. Use netconf (as root) to change the name of the machine.
whoami
Print my login name.
date
Print or change the operating system date and time
time
Determine the amount of time that it takes for a process to complete + other info.
uptime
Show the number days server has been up including system load averages.
uname -a
Displays info on about your server such as kernel version.
free
Memory info (in kilobytes).
lsmod
Show the kernel modules currently loaded. Run as root.
dmesg | less
Print kernel messages.
man topic
Display the contents of the system manual pages (help) on the topic. Do ‘man netstat’ to find all details of netstat command including options and examples.
reboot / halt
Halt or reboot the machine.
mount
Mount local drive or remote file system.
mount -t auto /dev/fd0 /mnt/floppy
Mount the floppy. The directory /mnt/floppy must exist.
mount -t auto /dev/cdrom /mnt/cdrom
Mount the CD. The directory /mnt/cdrom must exist.
sudo
The super-user do command that allows you to run specific commands that require root access.
fsck
Check a disk for errors
COMPRESSION UTILITIES
There are many other compression utilities but these are the default and most widely utilized.
tar
Creating and Extracting .tar.gz and .tar files
tar -zxvf file.tar.gz
Extracts the file
tar -xvf file.tar
Extracts the file
tar -cf archive.tar contents/
Takes everything from contents/ and puts it into archive.tar
gzip -d filename.gz
gzip -d filename.gz
zip
Compress files into.zip
unzip file.zip
Extracting .zip files shell command
compress
Compress files. compress filename
uncompress
Uncompress compressed files. uncompress filename.Z
bzip2
Compress files in bzip2 format
THE (DOT) FILES
The good old dot files. Let’s clear up some confusion here by defining each.
.bash_login
Treated by bash like .bash_profileif that doesn’t exist.
.bash_logout
Sourced by bash login shells at exit.
.bash_profile
Sourced by bash login shells after /etc/profile
.bash_history
The list of commands executed previously.
.profile
Treated by bash like ~/.bash_profile if that and .bash_login don’t exist.
.vimrc
Default “Vim” configuration file.
.emacs
Read by emacs at startup
CONFIGURATION FILES
Listing everything is beyond the scope of this article.
/etc
This directory contains most of the basic Linux system-configuration Files.
/etc/init.d
Contains the permanent copies of System V–style run-level scripts. These scripts are often linked to files in the /etc/rc?.d directories to have each service associated with a script started or stopped for the particular run level. The ? is replaced by the run-level number (0 through 6). (Slackware puts its run-level scripts in the /etc/rc.d directory.)
/etc/cron*
Directories in this set contain files that define how the crond utility runs applications on a daily (cron.daily), hourly (cron.hourly), monthly (cron.monthly), or weekly (cron.weekly) schedule.
/etc/cups
Contains files used to configure the CUPS printing service.
/etc/default
Contains files that set default values for various utilities. For example, the file for the useradd command defines the default group number, home directory, password expiration date, shell, and skeleton directory
/etc/skel
Any files contained in this directory are automatically copied to a user’s home directory when that user is added to the system.
/etc/mail
Contains files used to configure your sendmail mail service.
/etc/security
Contains files that set a variety of default security conditions for your computer.
/etc/sysconfig
Contains important system configuration files that are created and maintained by various services (including iptables, samba, and most networking services).
/etc/passwd
Holds some user account info including passwords (when not “shadowed”).
/etc/shadow
Contains the encrypted password information for users’ accounts and optionally the password aging information.
/etc/xinetd.d
Contains a set of files, each of which defines a network service that the xinetd daemon listens for on a particular port.
/etc/syslogd.conf
The configuration file for the syslogd daemon. syslogd is the daemon that takes care of logging (writing to disk) messages coming from other programs to the system.
/var
Contains variable data like system logging files, mail and printer spool directories, and transient and temporary files.
/var/log
Log files from the system and various programs/services, especially login (/var/log/wtmp, which logs all logins and logouts into the system) and syslog (/var/log/messages, where all kernel and system program message are usually stored).
/var/log/messages
System logs. The first place you should look at if your system is in trouble.
/var/log/utmp
Active user sessions. This is a data file and as such it can not be viewed normally.
/var/log/wtmp
Log of all users who have logged into and out of the system. The last command can be used to access a human readable form of this file.
Apache Shell Commands
Some of the basic and helpful apache commands.
httpd -v
Outputs the build date and version of the Apache server.
httpd -l
Lists compiled in Apache modules
httpd status
Only works if mod_status is enabled and shows a page of active connections
service httpd restart
Restarted Apache web server
MySQL Shell Commands
Some of the basic and helpful MySQL commands.
mysqladmin processlist
Shows active mysql connections and queries
mysqladmin processlist |wc -l
Show how many current open connections there are to mysql
mysqladmin drop database
Drops/deletes the selected database
mysqladmin create database
Creates a mysql database
mysql -u username -p password databasename < data.sql
Restores a MySQL database from data.sql
mysqldump -u username -p password database > data.sql
Backup MySQL database to data.sql
echo “show databases” | mysql -u root -p password|grep -v Database
Show all databases in MySQL server.
mysqldump -u root -p password database > /tmp/database.exp
Dump database including all data and structure into /tmp/database.exp
Thank You,
Preeti S
ThinkSupport.net