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If you have recently moved to WordPress from a hosted blogging solution like Blogger or TypePad, you may be unfamiliar with the tasks of managing a webspace as well as a blog. WordPress is based on PHP; many hosting services use servers running Linux and Apache; many web hosts offer not only web-based control interfaces to their customers but also shell access or command-line interfaces. Many WordPress users may not be familiar with using the shell to manage their file systems. This article explains the more commonly-used UNIX commands and demonstrates how a routine administrative task, namely a minor WordPress upgrade, is carried out in the shell.
The shell offered by your web host is likely to be bash, which stands for "Bourne Again Shell" after Stephen Bourne who wrote the original modern Unix shell. bash is distributed by the Free Software Foundation. There are a number of different Unix shells. The commands briefly described below apply to almost all of them.
The Secure Shell (ssh) is a complete set of tools for remote administration of your website. It includes SFTP (Secure File Transfer Protocol) for the uploading of files to your host. The main benefit of using ssh to interface with a remote server is increased security. With other server access tools, your login password may be transferred over the Internet in plain text, which may be intercepted.
On Linux or UNIX-based operating systems, you can use the text-based SSH and SFTP clients from terminals such as Konsole, Gnome Terminal or xterm. Graphical FTP clients such as KBear and gFTP also support sftp.Your hosting company will provide the username and host details (the "shell account") necessary to use these. They may be different from the ones you use with your control panel. To use, at the Terminal prompt type
sftp username@hostIf the SSH server you're connecting to is running on a non standard port, use the -p argument, followed by the port number. So, for example, if the remote server SSH was running on port 1000 you would type
ssh username@host -p 1000To use sftp to connect to a remote server on a non-standard port use the -oPort= argument. So, for example, to connect to a remote server using sftp on port 1000 you would type
sftp -oPort=1000 user@host
Before we get started with some UNIX commands, let's review some terminology.
"My Pictures"or as
The * and ? Symbols: The * and ? symbols are called wildcards and can be used in any command which deals with files. The * represents any number of characters. The ? represents just one. Note that Linux filenames are case-sensitive — the norm is lowercase. All commands are lowercase.
Command Options: Commands usually accept options or parameters, which are given in a sequence beginning with a hyphen (-). If you would want to set options b, r and f for a command, type
command -brfOther specifications, like file names, go after the options.
Here's a brief introduction to some useful UNIX shell commands.
This command displays a listing of a directory's contents. Unmodified, the command displays the contents of the current directory; you can also specify another directory's content to list. Some useful options are:
ls -l |less
The cd command changes the current directory. To switch from the current directory into a sub-directory, put the sub-directory's name after the command. To change into a sub-directory wp-content, you'd type
To move up into the directory above the current directory, type
To change from the current directory to your home directory, type
The mkdir command creates a new directory inside the current one. To create a directory named audio inside the current directory, type
To remove an empty directory, type rmdir directoryname for example:
If you want to create a directory, and one or more sub-directories within it, with a single command you can use the '-p' argument with the mkdir command.
For example, to create the directory 'maindir' and 3 sub-directories named 'sub1', 'sub2' and 'sub3' within it use the following command:
mkdir -p maindir/sub1 maindir/sub2 maindir/sub3
The rm command deletes ('removes') a file, a group of files, or a directory. When using this command, use extreme caution, as once you remove the file there is no good or consistent way to recover it.
To remove a single file use:
You can remove multiple files by naming them one after another on the line:
rm filename.php filename.html
You can also a group of files that have similar names with the use of a well place '*', and it will prompt you to type 'yes' to confirm each deletion:
To remove files without it prompting for confirmation, use the '-f' flag:
rm -f filename*
To remove an entire directory and its contents in one go, type:
rm -rf /path/to/directoryname.
Beware — once something is removed in this way, it is gone forever.
The exit command ends your shell session.
The mv command moves files from one place to a another; it is also used to rename files. Type
mv file new-location
If the new-location parameter is a (valid) directory in the current filesystem, the file is moved into that directory; if it isn't (and if it doesn't clash with an existing filename), the file will be renamed as new-location. You can also move and rename a file with one command:
mv file ~/path/to/new-file-name
The cp command copies files or directories. To copy a directory and its entire contents, use
cp -rf source-file destination
The ln command creates links. The links relevant to our purposes are "symbolic links" or symlinks — files which "point" to other files or directories in the filesystem. When you access a symlink, you are actually accessing the original file. If you want to change the location of your WordPress directory from, say, /wordpress/ to /blog/, you could create a symlink as follows:
ln -s wordpress blog
Access will then be through either the file or directory's actual name — wordpress — or through the link name — blog. In the Options panel in the Wordpress Administration Panels, set the "Blog address (URI)" field to show the symlink rather than the name of the directory.
The tar and unzip commands are used to compress and decompress "archive" files. Archives are files or folders that have been "compressed" — i.e. reduced in file-size — and are commonly used for distribution and backup purposes. The unzip command is used for files ending with .zip; the tar command is used for files ending with .tgz or .tar.gz.Unzipping files: If the file is a .tar.gz archive, type
tar -zxvf file.tar.gz
If it's a zip archive, you may need to create a temporary directory into which you'd unzip its contents (its files might be unzipped into the current directory otherwise).If the file is a .tar.bz2 (bzip2) archive, use the following command to extract its contents
tar -xjvf file.tar.bz2
The chmod command changes the permissions on a given file. UNIX file permissions specify who can do what with a given file. The ls -l command will tell you what permissions a file or directory has:
-rw-r--r-- 1 domain60 vweb 840 Feb 21 06:38 wp-config-sample.php -rw-r--r-- 1 domain60 vweb 826 Jun 29 20:31 wp-config.php drwxr-xr-x 4 domain60 vweb 4096 Jun 29 20:30 wp-content -rw-r--r-- 1 domain60 vweb 762 Mar 29 16:05 wp-feed.php drwxr-xr-x 3 domain60 vweb 4096 Jun 29 18:46 wp-images drwxr-xr-x 2 domain60 vweb 4096 Jun 29 18:46 wp-includes
The permissions are displayed in the string of letters in the first column. The very first letter of that column indicates whether it is a file, a link, or a directory. A d denotes a directory, a l denotes a link, a hyphen denotes a file.
The permissions are declared with the following nine letters, which are shown in groups of three. The first group of three concerns the owner, the second the group he belongs to (this is unlikely to concern you as a web host user), and the third concerns everyone else. Note that people with root access (administrators) have access to all files on the system.
The letters r, w and x stand for read, write and execute; if the file is a directory, executable means traversible, that is, that you can move into that directory with the cd command. Where a hyphen is shown in the permissions list, the permission is absent.
You change permissions with the chmod command. You may, in fact, not have to change the permissions at all; some hosts automatically set certain permissions on any file in the web directory. Your host may also tell you what permissions need to be set on your server.The chmod command can be used to set permissions in two ways: with letters or with numbers. If you use letters, you could type
chmod o+w filename
This grants write privileges to everyone with access to the system. The first letter can be u (user), g (group) or o (other), or a combination; the + (grant) can also be - (withhold), and the third can also be r or x (read or execute).
If you use numbers, all permissions for a file are set in one go. An example:
chmod 755 wp-images
sets the permssions of the wp-images directory to 755, whereby the first number (the "hundreds") is for the user, the second (the "tens") is for the group and the third (the "units") is for everyone else.
More about numerical permissions settings: To add 4 in any of the fields grants read privileges; to add 2 grants write and to add 1 grants executability; each combination has a unique number. The directories in the example above have the permission set 755, which is common for web-available directories, in which the user has full privileges while others have read and execute only; the files in the example have the permission set 644, in which the user can read and write while others can only read.
6 4 4 420400400 -rw-r--r-- 1 domain60 vweb 840 Feb 21 06:38 wp-config-sample.php 7 5 5 421401401 drwxr-xr-x 2 domain60 vweb 4096 Jun 29 18:46 wp-includes
The screen command allows you run multiple console-based applications with in a single Terminal session. If GNU screen is installed on your server, you can use the following command to start it:
When screen starts, a welcome message should be displayed. Just press Return to get rid of this message and you should now see a shell prompt. This will be the first session window and is numbered 0. Each subsequent new session you open will be given a number, starting from 1 for the second session window.
To create a new session window press CTRL-a then C
To switch between currently open session windows press: CTRL-a followed by the number corresponing to the session window you want to access.
To get a list of all the session windows that are currently open press: CTRL-a
To exit screen altogether, stop all running programs and type exit at the shell prompts in all the session windows you have opened (including window '0'). screen will terminate when there are no more programs running in any open session windows.
Let's use the example of upgrading WordPress using the command line. First, establish the location of your WordPress on your web server's filesystem. This example assumes it is located at ~/public_html/blog.
wget http://wordpress.org/latest.tar.gz tar -zxvf latest.tar.gzThe WordPress archive will be unpacked into a new directory named /wordpress.
rm wp-config-sample.php(We will use our current wp-config.php instead)
rm -rf wp-content
cp ~/public_html/blog/wp-config.php . cp ~/public_html/blog/.htaccess .Note: Don't forget the dot at the end of both commands!
cp -rf ~/public_html/blog/wp-content/ .Again, note the dot at the end of the command.
rm -rf ~/public_html/blog/*
cp -rf * ~/public_html/blog
SFTP stands for Secure File Transfer Protocol. It is an encrypted replacement for FTP, and as with FTP, you may use a shell-based client or one of the graphical clients mentioned at the top of this article. If your host supports SSH, it also supports SFTP.
Shell-type SFTP clients support commands similar to those used in bash. These include cd, ls, mkdir, rm and rmdir. It also supports ln, with the difference that you do not need to use the -s option to create symlinks; in sftp, the ln command makes symlinks by default. All of these work on files on your host's system.
These two commands transfer to your host (i.e. upload) a single file (put) or any files that match the pattern you supply (mput); the wildcards * and ? described above can be used here.
These two commands transfer from your host to your local computer (i.e. download) a single file (get) or any files that match the supplied pattern (mget). As with mput, * and ? can be used.
These commands are identical to their bash shell counterparts: change the current directory, make a new directory, and list the contents of the current directory. To do the same things within SFTP on your own machine, add an l to the front of the commands: lcd, lmkdir, lls.