The following is a list of UNIX commands that you might find helpful when
modifying your web sites on the server. Most UNIX commands have many options and parameters which are
not listed here. For more complete information on using UNIX commands, you can refer to the online
manual by typing man [command] at the UNIX prompt, where "[command]" represents the command you
would like more information about. Other UNIX help commands you can type are [command] -? and
[command] --help.
Note: When something is
specified in brackets, such as [command] or [filename], it is used to indicate that you
must input your desired information here. Do NOT include brackets in your command.
Navigating in UNIX
| pwd |
Shows the
full path of the current directory |
| ls |
Lists all
the files in the current directory |
| ls -al |
Lists all
files and information |
| ls –alR |
Lists all
files and information in all subdirectories |
| ls -alR
| more |
Same as
ls –alR, pausing when screen becomes full |
| ls -alR
> filename.txt |
Same as
ls –alR, outputs the results to a file |
| ls -al
/home/usr/bob/ |
Lists
files and information for /home/usr/bob |
| ls
*.html |
Lists all
files ending with .html |
| cd
[directory name] |
Changes
to a new directory |
| cd .. |
Changes
to directory above current one |
Moving, Copying and Deleting Files
| mv
[old filename] [new filename] |
Move/rename a file |
| cp
[filename] [new filename] |
Copies a
file |
| rm
[filename] |
Deletes a
file |
| rm * |
Deletes
all files in current directory |
| rm
*.html |
Deletes
all files ending in .html |
Creating, Moving, Copying and Deleting Directories
| mkdir
[directory name] |
Creates a
new directory |
| ls -d
*/ |
Lists all
directories within current directory |
| cp -r
[directory] [new directory] |
Copies a
directory and all files/directories in it |
Searching Files and Directories
| find .
-name [filename] -print |
Searches
for a file starting with current directory |
| grep
[text] [filename] |
Searches
for text within a file |
File and Directory Permissions
There are three levels of file permissions: read, write
and execute. In addition, there are three groups to which you can assign permissions: file owner,
user group and everyone. The command chmod followed by three numbers is used to change
permissions. The first number is the permission for the owner, the second for the group and the
third for everyone. Here are how the levels of permission translate:
| 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 |
It is preferred that the group always have permission of 0. This
prevents other users on the server from browsing files via Telnet and FTP. Here are the most
common file permissions used:
| chmod
604 [filename] |
Minimum
permissions for HTML file |
| chmod
705 [directory name] |
Minimum
permissions for directories |
| chmod
755 [filename] |
Minimum
permissions for scripts & programs |
| chmod
606 [filename] |
Permissions for data files used by scripts |
| chmod
703 [directory name] |
Write-only permissions
for public FTP uploading |
Scheduling Tasks ("Cron")
You can schedule tasks to run automatically by using the UNIX cron command. To use this, you create
a text file with cron instructions, then process this file. cron instructions are basically UNIX
commands with extra info about the time that they will run.
One important thing to note is that it is best to use full paths when creating your cron file. As an
example, create a file called mycronfile and in it place one line:
0 1 * * * cp /usr/www/file.txt /usr/www/backup.txt
now at the command line, type the following:
crontab mycronfile
You have just scheduled an automated task! This task will run at the time specified until you decide
you want to cancel it. There are six fields in this file. The first five represent the time that the
job will run. The sixth field is a UNIX command that will run at the specified time. The above example
will run every night at 1AM, at which time it will copy a file.
Here is how the fields break down:
Field 1 | Field 2 | Field 3 | Field 4 | Field 5
Minutes | Hours | Day of Month | Month | Day of Week
(0-59) | (0-23) | (1-31) | (1-12) | (0-6)
You can enter a number in the field, a range of numbers, or an * to indicate all. Here are a few
more examples. These examples use the ls command, which would be pretty useless. Note the time that it
runs, though.
0 1 * * 1-5 ls (this would run every Monday-Friday at 1am)
0 1 * * 1,3,5 ls (this would run every Monday, Wednesday and Friday at 1am)
10 2 1 * * ls (this would run at 2:10am on the first of every month)
0 1 1 1 * ls (this would run at 1am on January 1 every year)
If you have a more complicated command that you want to run, it is sometimes helpful to create a
shell script and have that script run. You specify the shell script as you would any UNIX command. For
example:
0 1 * * * /usr/www/myscript
There are some other crontab switches that are useful:
crontab -l (lists your currently scheduled tasks)
crontab -r (delete all currently scheduled tasks)
crontab -e (directly edit your scheduled tasks)
Please note that excessive cron use - for instance a processor-intensive script that is run every
hour - may consitute a violation of the Acceptable Use Policy. As a general rule we ask that you have
cron tasks run no more than twice per 24 hour period. |
