Creating and Editing crontab Files

The simplest way to create a crontab file is to use the crontab -e command. This command invoke the text editor set up for your system environment, which is defined by the EDITOR environment variable. If this variable has not been set, crontab uses the default editor, ed. Preferably, you should choose an editor that you know well.

The following example shows how to determine if an editor has been defined, and how to set up vi as the default.

$ which $EDITOR
$ 
$ EDITOR=vi
$ export EDITOR

When you create a crontab file, it is automatically placed in the /var/spool/cron/crontabs directory and is given your user name. You can create or edit a crontab file for another user, or root, if you have superuser privileges.

How to Create or Edit a crontab File

1. (Optional) Become superuser to create or edit a crontab file that belongs to root or another user.

2. Create a new crontab file, or edit an existing one.

   $ crontab -e [username]

   Where username specifies the name of the user's account for which you want to create or edit a crontab file. To create or edit crontab files requires superuser privileges.

   ---

   Caution –

   If you accidentally type the crontab command with no option, press the interrupt character for your editor. This character allows you to quit without saving changes. If you instead saved changes and exited the file, the existing crontab file is overwritten with an empty file.

   ---

3. Add command lines to the file.

   Follow the syntax described in Syntax of crontab File Entries. The crontab file will be placed in /var/spool/cron/crontabs.

4. Verify your crontab file changes.

   # crontab -l [username]

Example—Creating or Editing a crontab File

The following example shows how to create a crontab file for another user.

# crontab -e jones

The following command entry added to a new crontab file automatically removes any log files from the user's home directory at 1:00 a.m. every Sunday morning. Because the command entry does not redirect output, redirect characters are added to the command line after *.log to make sure that the command executes properly.

# This command helps clean up user accounts.
1 0 * * 0 rm /home/jones/*.log > /dev/null 2>&1

How to Verify a crontab File

To verify that a crontab file exists for a user, use the ls -l command in the /var/spool/cron/crontabs directory. For example, the following display shows that crontab files exist for users smith and jones.

$ ls -l /var/spool/cron/crontabs
-rw-r--r--  1 root     sys          190 Feb 26 16:23 adm
-rw-------  1 root     staff        225 Mar  1  9:19 jones
-rw-r--r--  1 root     root        1063 Feb 26 16:23 lp
-rw-r--r--  1 root     sys          441 Feb 26 16:25 root
-rw-------  1 root     staff         60 Mar  1  9:15 smith
-rw-r--r--  1 root     sys          308 Feb 26 16:23 sys

Verify the contents of user's crontab file by using the crontab -l command as described in How to Display a crontab File.