formats

Ssh Commands

Published on December 10, 2012, by in Uncategorized.

Overview

This article is an introduction to finding your way around your server in SSH. It takes a Day 1 approach to SSH.

  • Hit Enter or Return after every command unless specified otherwise.
  • The domain example.com should always be replaced with your own domain name.
  • Whenever you see 00000, you should replace it with your site number.
  • Example paths and file names should also be replaced with your own server information.

Requirements

This article assumes that:

  1. You have enabled your SSH user, which should be the same as your primary domain.
  2. You have used Terminal (Mac) or PuTTY (Windows) to log into the server. You should be looking at a command prompt.

If you need help with these steps, please see: Connecting via SSH to your server.

READ ME FIRST

This article is provided as a courtesy. Installing, configuring, and troubleshooting third-party applications is outside the scope of support provided by (mt) Media Temple. Please take a moment to review the Statement of Support.

Home and navigation

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

  • This is /home/00000/users/.home/.

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 /home/00000/domains/example.com/.

TIP:

On the (gs) Grid-Service, you can’t do anything above your server directory. For practical purposes, you will always be in /home/00000/ or lower. However, starting your paths from / can still be useful for navigation.

Your home directory is two levels below your server directory. If you want to see the same folders that you see in FTP, run this command when you first log in:

cd /home/00000/

Or, if you don’t want to look up your site number, this command will jump you up two levels:

cd ../..

Common paths:

  • /home/00000/domains/example.com/html/ – web document root
  • /home/00000/logs/ – per-domain access and error logs
  • /home/00000/etc/ – location of php.ini file

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 /home/00000/domains/

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:

/home/00000/data/

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-xr-x 3 example.com example.com 15 Oct 21 10:01 . 
drwxr-xr-x 6 example.com example.com 6 Oct 21 09:13 .. 
-rw-r--r-- 1 example.com example.com 137 Oct 21 10:01 .htaccess 
drwxr-xr-x 2 example.com example.com 4 Jun 8 17:24 errors 
-rwxr-xr-x 1 example.com example.com 379 Jan 28 2010 hello.pl 
-rw-r--r-- 1 example.com example.com 45 Oct 30 2009 home.html 
-rw-r--r-- 1 example.com example.com 83 Oct 21 09:47 index.php 
-rw-r--r-- 1 example.com example.com 68 Jul 20 15:53 phpinfo.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 example.com example.com 83 Oct 21 09:47 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.
  • example.com – The owner of this file.
  • example.com – The group this file belongs to. May also be www-data.
  • 83 – The size of this file.
  • Oct 21 – The date this file was last modified.
  • index.php – The name of this file.

Change permissions

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. Click here for a table of numbers and permissions. 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.

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/ ..

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

 

  • 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):

(Just replace 00000 with your own site number, the rest works as-is):

find /home/00000/ -noleaf -type f -size +10000k 2>/dev/null -exec ls -lh {} \; | awk '{ print $5 ": " $9 }' |sort -n

MySQL access

Run this command to log into MySQL:

mysql -h internal-db.s00000.gridserver.com -u username

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

Log Files

Log files can tell you a lot about what’s happening on your (dv) Dedicated-Virtual 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 /home/00000/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 /home/00000/logs/error_log

Log locations

  • Apache error log for your domain:

/home/00000/logs/error_log

  • Statistic log for your domain:

/home/00000/logs/access_log-YYYY-MM-DD-##.processed

  • SSH history – just type:
history
  • You will need to enable your error log before it is available.
  • To gain access to individual user directories and email accounts, you will need to enable SSH for that email user. See Add email userfor instructions on accessing your email users. The login for these users is of the following form:
    ssh username%example.com@example.com

Final tips

  • When you are typing a path or file name, hit “Tab” after the first few letters. If it’s the only file or folder matching the letters you’ve typed, the rest of it will auto-complete.
  • Hit the up arrow to scroll back through previous commands – save yourself some typing!
  • Always make a backup copy of the working version of a file before editing it.
  • q or CTRL-C usually gets you out of any special mode you might be in.
  • If you’ve encountered an unknown command, type “man” and then the command name to learn more about it. (Example: man ls) This will also show you special options like the -alh option for the list command.
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