SSH (Secure Shell)

Posted by Ben Harris

Like many people, I use Secure Shell (SSH) quite a lot with the linux shell. The following are some commonly used commands, what they do, and some basic usage. To use SSH, most people use a small standalone application called PuTTY, which can be found here.

ls : Lists files and directories within the current directory
ls -l : Lists files, permissions, owner, date modified and filesize

cd : Change directory.
Used as cd /home/username/public_html/ (apsolute path) or
Used ad cd public_html (relative path)
cd
~ : Takes you to your home directory (on cpanel servers this is usually /home/username)
cd ../ : Takes you to the directory above you.

cat filename : shows the contents of filename.

chmod : Change file access permissions for USER - GROUP - EVERYONE.
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

Example Usage:
chmod 777 filename
This gives the USER, GROUP and EVERYONE Read, Write and Execute permissions for the file named filename.

Common Usage
chmod 000
: No-one can access the file
chmod 644 : Default for most files
chmod 755 : Used for CGI scripts and directories
chmod 777 : Usually used if you want a script to write to a file

pico : Easy to use file editor.
Used as follows: pico filename

grep : Looks for patterns within files.
Used as follows: grep “what your looking for” /file/location or

Used as: cat /proc/cpuinfo | grep “vendor_id” this would show the line that shows the vendor_id within the file /proc/cpuinfo.

last : shows the last users that logged in. Can also use last -20 -a which would show the last 20 logins with hostnames

w : shows users that are logged in with where they are logged in from

who : Shows who is on the server in a shell

users : Shows users logged into shell

netstat : Shows all current network connections

top : Shows all live system processes, uptime, memory stats etc.. (The processes are show in a style similar to the Windows Task Manager).

touch : Creates an empty file.
Used as follows: touch /path/to/where/you/want/the/file/filename.html

du -sh : Shows disk usage in a readable format.

cp filename filename.copy : Would copy the file filename to filename.copy So there would now be 2 files called filename and filename.copy.

mv filename newdir/filename : Would move filename to the the directory named newdir. You can also change the destination filename to something diferent, so for example mv filename newdir/filename2 would move filename into newdir, and rename it filename2.

rm filename : Remove/Delete file called filename.

tar : Creating and Extracting tar and tar.gz files

Usage:
tar -zxvf file.tar.gz : Extracts the file file.tar.gz (Gzipped)
tar -xvf file.tar : Extracts the file file.tar (Not Gzipped)

tar -cf archives.tar directory/ : Takes everything from directory/ and puts it into archives.tar

unzip filename.zip : Extracts filename.zip into the current directory.

zip filename.zip filename : Zip filename into a zip file called filename.zip

logout : closes the session.

exit : exits the session (basically the same as logout)

This covers the major commands.

Regards

Ben Harris

Posted in: Linux Comments(0) February 2008