Common SSH and Linux Shell Commands

Some valued linux commands, you can read them all with the following format on most Linux systems. Please not $ is for user access and # is for root user. You will see these symbols in your command prompt.
$ man (software)
example $ man netstat

File Manipulation

ls : list files/directories in a directory, comparable to dir in windows/dos.
ls -al : shows all files (including ones that start with a period), directories, and details attributes for each file.
ls –alR —- Lists All Files & Information In All SubDirectories

cd : change directory
cd /usr/local/apache : go to /usr/local/apache/ directory
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 : cat the contents of filename.txt to your screen

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/

ln : create’s “links” between files and directories
ln -s /home/username/tmp/webalizer webstats : Now you can display http://www.yourdomain.com/webstats to show your webalizer stats online. You can delete the symlink (webstats) and it will not delete the original stats on the server.

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. BE VERY CAREFULL WITH THIS COMMAND!!!
cp : copy a file
cp filename filename.backup : copies filename to filename.backup
cp -a /home/burst/new_design/* /home/burst/public_html/ : copies all files, retaining permissions form one directory to another.
find * -type d|xargs -i cp --verbose php.ini {} : copies your php.ini file into all directories recursively.

kill : terminate a system process
kill -9 PID EG: kill -9 431
kill PID EG: kill 10550
Use top or ps ux to get system PIDs (Process IDs)

EG:

PID TTY TIME COMMAND
10550 pts/3 0:01 /bin/csh
10574 pts/4 0:02 /bin/csh
10590 pts/4 0:09 APP

Each line represents one process, with a process being loosely defined as a running instance of a program. The column headed PID (process ID) shows the assigned process numbers of the processes. The heading COMMAND shows the location of the executed process.

MySQL Dump
mysqldump -u username -p dbname > file.sql

Importing MySQL database
mysql -u username -p database_name <file.sql

View Information

tail : like 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

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

more : like cat, but opens the file one screen at a time rather than all at once
more /etc/userdomains : browse through the userdomains file.
hit Space to go to the next page, q to quit

grep : looks 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

w : shows who is currently logged in and where they are logged in from.

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.

top : shows live system processes in a nice table, memory information, uptime and other useful info.
This is excellent for managing your system processes, resources and ensure everything is working fine and your server isn’t bogged down.
top
Shift + M to sort by memory usage
Shift + P to sort by CPU usage

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!

file : attempts to guess what type of file a file is by looking at its content.
file * : prints out a list of all files/directories in a directory

du : shows disk usage.
du -sh : shows a summary, in human-readable form, of total disk space used in the current directory, including subdirectories.
du -sh * : same thing, but for each file and directory. helpful when finding large files taking up space.

wc : word count
wc -l filename.txt : tells how many lines are in filename.txt

which [perl] or [PHP]
Finding path to [perl] or [PHP] etc

netstat -an |grep :80 |wc -l
Show how many active connections there are to apache (httpd runs on port 80)

mysqladmin processlist |wc -l
Show how many current open connections there are to mysql

Putting Commands Together

Often you will find you need to use different commands on the same line. Here are some examples. Note that the | character is called a pipe, it takes date from one program and pipes it to another.
> means create a new file, overwriting any content already there.
>> means to append data to a file, creating a new one if it doesn’t already exist.
< send input from a file back into a command.

tail -10000 /var/log/exim_mainlog |grep domain.com |more
This will grab the last 10,000 lines from /var/log/exim_mainlog, find all occurances of domain.com
(the period represents ‘anything’, comment it out with a so it will be interpretted literally), then send it to your screen page by page.

Edit Information

pico : friendly, easy to use file editor
pico /home/burst/public_html/index.html : edit the index page for the user’s website.

vi : another editor, tons of features
vi /home/burst/public_html/index.html : edit the index page for the user’s website.

Compression

unzip [filepath.zip]—-Unzips A .ZIP File
tar -xvf [filepath.tar]—-Untars A .TAR File
gzip -d [filepath.gz]—-Ungzips A .GZIP File
gzip -d filepath.tar.gz—-Ungziptar’s A .TAR.GZ File
tar -xvf filepath.tar

Permissions

0 = — No Permission
1 = –X Execute-Only
2 = -W- Write-Only
3 = -WX Write & Execute
4 = R– Read-Only
5 = R-X Read & Execute
6 = RW- Read & Write
7 = RWX Read, Write & Execute

You Need To Set This On Files For:

Owner – The File Owner
Group – People On The Server
User – Everyone

It’s normally best if you want to keep a file really secure, to keep Group as “0” to stop people on the server from looking/changing it!

Commonly Used Commands

ping
ls
less
vi
nano
ifconfig
awk
grep
top
dh
free
whoami
who
nslookup
host
traceroute

Author: Christopher Smith

I managed websites.

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