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.
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
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
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
pico : friendly, easy to use editor. A clone of it is "nano"
pico /home/burst/public_html/index.html : edit the index page for the user's website.
vi : another editor, tons of features, harder to use at first than pico
vi /home/burst/public_html/index.html : edit the index page for the user's website.
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
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 /usr/local/apache/conf/httpd.conf /etc/httpd.conf : Now you can edit /etc/httpd.conf rather than the original. changes will affect the original, however you can delete the link and it will not delete the original.
rm : delete (remove) 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!!!
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
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.
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
du : shows disk usage.
du -sh : shows a summary, in human-readble 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
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.
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 data 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 does not already exist.
< send input from a file back into a command.
grep User /usr/local/apache/conf/httpd.conf |more -- this will dump all lines that match User from the httpd.conf, then print the results to your screen one page at a time.
last -a > /root/lastlogins.tmp -- this will print all the current login history to a file called lastlogins.tmp in /root/
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 interpreted literally), then send it to your screen page by page.
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
sudo -- allows users to run programs with the security privileges of another user