Common SSH Commands

BySam

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When you first log into your server, you will be in your home directory.

  • For the root user, this is /root/.

Linux folder structure

Linux uses a nested folder structure to store different files. The top-level directory is considered the root directory, and is designated by /. Folders beneath the root level are separated by slashes. For example, all of your website content is located in /var/www/vhosts/example.com/.

TIP:

Remember that / is not the same as /root/. The / is the root level of the server. You cannot get any higher than that. The home directory for the user called root is /root/.

Common paths:

  • /var/www/vhosts/example.com/httpdocs/ – web document root
  • /var/www/vhosts/example.com/statistics/logs/ – per-domain access and error logs
  • /var/www/vhosts/example.com/conf/ – per-domain configuration files
  • /etc/ – configuration files
  • /etc/init.d/ – software daemon start files

Move into another directory

Use this command to move into a directory:

cd

You can specify the full path from the root of the server:



cd /var/www/vhosts/example.com/conf/


You can type the path from where you are now (leave out the beginning /):


cd downloads/


You can go up a directory level:


cd ..


You can go to your home directory:


cd ~


Where am I?


Working with your server without graphics can take a little getting used to. If you ever need to see exactly which folder you’re in, use the following command:


pwd


It stands for print working directory. You’ll see output like this:




/var/www/vhosts/


What’s here?


Next, we want to see a list of files and folders in our current directory:


ls -alh


ls is the list command, and -alh modifies the standard list in three ways. a means that all files, even hidden files, should be shown. l means that the long format is used – it shows things like file size and the date every file was last modified. h makes the sizes display in convenient units. Here’s some sample output:




drwxr-x--- 10 domainuser psaserv 4.0K Oct 20 19:51 .
drwxr-xr-x 14 root       root    4.0K Aug 17 22:16 ..
-rw-r--r--  1 domainuser psacln    58 May 31 22:49 .htaccess
-rw-r--r--  1 domainuser psacln  2.1K Apr 20  2010 about.php
-rw-r--r--  1 domainuser psacln   907 Feb 25  2010 archive.php
drwxr-xr-x  2 domainuser psacln  4.0K Jul  2 16:43 image
-rw-r--r--  1 domainuser psacln  1.9K Mar  5  2010 index.php



Files


Let’s break down the elements of a file that are displayed when you run the ls -alh command from the previous section.




-rw-r--r--  1 domainuser psacln  1.9K Mar  5  2010 index.php


    

  • -rw-r–r– – These are the permissions for this file. r stands for “read,” w stands for “write,” and x stands for “execute.” The first character is standalone, and the next nine are in groups of three: the first triplet (rw-) applies to the owner, the second (r–) to the group, and the third (r–) to everyone. So, in this example, the owner has read and write access, the group just has read access, and everyone has read access. See File Permissions for an in-depth discussion.
    • 

  • 1 – Number of links to this file.
    • 

  • domainuser – The owner of this file.
    • 

  • psacln – The group this file belongs to.
    • 

  • 1.9K – The size of this file.
    • 

  • Mar 5 2010 – The date this file was last modified.
    • 

  • index.php – The name of this file.
    • 



Change permissions, owner, and group




This section shows basic commands for changing the access settings on a file. It is highly recommended that you read File Permissions before making any changes, so you’ll know what kinds of changes are good and what might be a security risk.


To change permissions:


chmod 755 index.php


chmod is the command. 755 is a code which tells what kinds of read, write, and execute permissions you want for the file. index.php is an example – you should replace with your file name.




Quick permissions guide:


7 = Read + Write + Execute

6 = Read + Write

5 = Read + Execute

4 = Read

3 = Write + Execute

2 = Write

1 = Execute

0 = All access denied


First number is for the owner, second for the group, and third for everyone.






To change owner:


chown domainuser index.php


chown is the command, short for “change owner.” domainuser is an example of a possible owner name – you should substitute this with your desired owner name. Note that the owner must exist on the server. index.php is an example – you should replace with your file name.


To change group:


chgrp psacln index.php


chgrp is the command, short for “change group.” psacln is an example of a common Plesk group – you should substitute this with your desired group name. Note that the group must exist on the server.


Change owner and group at once:


chown domainuser:psacln index.php


This command is exactly like the previous chown example, except that the group is also specified, after a colon (:).






Copy file


Use this command to copy a file to a different location (first example), or to the same folder but with a new name (second example):


cp logo.png image/logo.png


cp index.php index.php_old


cp is the command. The first file listed is the one you want to copy. The second file is the new name for the copied version of the file, including any path information for where the copy should be located. You can use a relative path like in the example above (that is, there is an image folder inside your current folder already), or you can use a full server path starting with /.


You can also copy an entire folder (along with all subfolders) using -R:


cp -R image/ image2


Move or rename file


The format for the move command is very similar to that for the copy command. Here’s an example:


mv logo.png image/logo.png


mv is the basic command. This moves logo.png into the image/ subdirectory.


You can also use it to rename a file:


mv index.php index.php_old


This renames index.php to index.php_old.


Finally, you can move a folder just as easily as a single file. This example shows how to move the folder image/ up one level (.. means “up one level”):


mv image/ ..






Compressing and decompressing a file using zip


Use this command to compress a file:


zip -r archive_name.zip folder_to_compress


Use this command to decompress a file:


unzip archive_name.zip


In these examples, zip and unzip are the commands. The -r option tells the command to work recursively. The archive_name.zip listed is the name of the file. Lastly, folder_to_compress is the directory you wish to compress.


Rsync


The rsync command can be used instead of the cp command, and works on all platforms of linux. Rsync can be used in the same way as cp with added benefits such as file permission and ownership preservation, compression during transfer, and comparison between files for updates to back ups.


rsync -a logo.png images/logo.png


rsync -a index.php index.php_old


rsync is the command, followed by the ‘-a’ flag which lets the system know to preserve the permissions, ownership, timestamp, and if rsyncing a directory, to do it recursively. The next part, ‘logo.png’ is the source file followed by the destination for that file to be copied to.


Another use for rsync is the ability to copy files and folders over a network to another server. This can be very helpful if you want to run some back ups, or migrate from one server to another within the (mt) Media Temple network. This first example will show you how to copy the entire document root for example.com to another server using it’s SSH login credentials.


rsync -avz example.com user@host:/path/to/destination


When you hit enter, you will be prompted to enter in the password for user on the remote server. This will move the entire directory, example.com and it’s contents over to the destination on the remote server. The options, ‘-avz’ let rsync know that you want to archive the file permissions, ownership, get a verbose readout of what file is being processed, and you would like to compress the files in order to use less bandwidth.


You can also reverse this to download a copy of files from a remote server to your local machine.


rsync -avz user@host:/path/to/source ./


Once again, you will be prompted for the password for the user account on the remote server. This will copy the specified file from the remote server to the current working directory on your local machine.






Create or edit a file


    

  • Create or edit a file:
    • 



vi file.html


If this is a new file, it’ll be empty when you open it, and you can start adding content. If this is an existing file, you’ll see its contents, which you can now edit.




vi tip: Press “i” to enter “insert mode” so you can type and copy/paste. Use the arrow keys to move back and forth in the file. Press “Esc” to exit “insert mode” when you are done modifying the file. Type “:wq” to save and quit.


See Understanding basic vi (visual editor) for more details.




    

  • Create an empty file (which you can later open for editing):
    • 



touch new_file.html


If you use an existing file name, it will instead “touch” that file and update its last-modified date.




Files are created with the owner and group of your SSH user. Once you’ve created a new file, it’s a good idea to run ls -alh to make sure its ownership matches the rest of the files in the directory. If not, run the chown command from the earlier section.




Read or search within a file


If you need to look through a file, the quickest way to get all the contents on your screen is cat:


cat index.html



<html>
<head>
<title>Home</title>
</head>
<body>
<p>Hello, world!</p>
</body>
</html>



However, this can be overwhelming if you have a large file. In that case, you can use less or | more to conveniently scroll through the content. less uses the arrow keys, and more uses Enter. Type q to exit either of them.


less access_log


cat access_log | more


    

  • Search files for a specific phrase:
    • 



cat error_log | egrep "permission"


This will list only the lines containing the word “permission.” cat shows the contents. Next, type the name of the file. | means the output should be filtered through the next command. egrep does the search. Your search term should go in quote marks, just in case it has special characters.






Delete file


You can also delete a file using SSH. Be sure you don’t need it any more before you delete it.


rm index.php_old


You will receive output like the following:


rm: remove regular file `index.php_old'? 


Type y confirm, or n to cancel. If you don’t want to be prompted, add -f to the command:


rm -rf index.php_old


Also, if you want to remove an entire directory and all its contents, including subdirectories, add -r. It can become tedious quickly to approve every deletion in a directory, so -f is commonly used.




Please be cautious with the rm -rf command. It will irreversibly delete a folder and all of the files and subfolders in it.


To make sure you’re deleting the right thing, you can always run a list command first. For example:


ls -alh /path/to/unwanted/folder/




Here’s the recursive deletion command:


rm -rf /path/to/unwanted/folder/




Disk use


    

  • Total server disk use:
    • 



df -h


You will see output like this, with an amount used and a percent used:


Filesystem            Size  Used Avail Use% Mounted on
/dev/vzfs              20G  3.1G   17G  17% /
simfs                  20G  3.1G   17G  17% /tmp
simfs                  20G  3.1G   17G  17% /var/tmp


    

  • Show all folder sizes for the current directory recursively, with their sizes:
    • 



du -h


If you run this from a high-level directory, it can take a while to complete.


    

  • Show a disk use summary for the current directory:
    • 



du -sh


Again, this can take a little while if you’re running it in a high-level directory.


    

  • Here’s an advanced find command you can run to find files over 10 MB (no variables in this one, just copy and paste):
    • 





find / -mount -noleaf -type f -size +10000k -print0 | xargs -0 ls -lhSr | awk '{printf "%*s %s\n",7,$5":",$9}'




DV server administration






Plesk admin password


    

  • Show Plesk admin password:
    • 



cat /etc/psa/.psa.shadow




MySQL access




The DV server has a simple shortcut for logging into MySQL:


my


Type quit to exit.


If you want to export or import a database, see Export and import MySQL databases.


Processes and system services


    

  • Show current server processes:
    • 



ps -auxf


    

  • Show processes and memory use live:
    • 



top


    

  • Start/Stop Services:
    • 





/etc/init.d/httpd restart


This example restarts Apache. You can also use start and stop. See Restart Plesk services for a list of services./span> 




    

  • Check Bean Counters for system resource limits (hard and soft limits, failcounts, etc.):
    • 



cat /proc/user_beancounters


For an explanation of the results of several of these commands, and for more advanced resource tracking and troubleshooting, consider reading Troubleshooting DV Memory Issues.


Log Files


Log files can tell you a lot about what’s happening on your DV server. Log files are generally very long, so you should use one of these commands to sort through them easily:


    

  • Show the most recent 100 lines of the file:
    • 





tail -n 100 /var/www/vhosts/example.com/statistics/logs/error_log


    

  • Watch this file live. Interact with your server (by trying to reproduce the error, or navigating your website) while this is running and watch the log file update. Use CTRL-C to exit.
    • 





tail -f /var/www/vhosts/example.com/statistics/logs/access_log


Log locations


    

  • Apache error log for your domain:
    • 



/var/www/vhosts/example.com/statistics/logs/error_log


    

  • Statistic log for your domain:
    • 



/var/www/vhosts/example.com/statistics/logs/access_log


    

  • Server error log:
    • 



/var/log/messages


    

  • Apache error log:
    • 



/var/log/httpd/error_log


    

  • MySQL logs:
    • 



/var/log/mysqld.log


    

  • Mail logs:
    • 



/usr/local/psa/var/log/maillog


    

  • SSH history – just type:
    • 



history





	

	





			

			

				

					
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