System Administration Guide: Advanced Administration

Creating and Editing crontab Files

The simplest way to create a crontab file is to use the crontab -e command. This command invokes the text editor that has been set for your system environment. The default editor for your system environment is defined in the EDITOR environment variable. If this variable has not been set, the crontab command 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
$ 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.

ProcedureHow to Create or Edit a crontab File

Before You Begin

If you are creating or editing a crontab file that belongs to root or another user you must become superuser or assume an equivalent role. Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services.

You do not need to become superuser to edit your own crontabfile.

  1. Create a new crontab file, or edit an existing file.

    $ crontab -e [username]

    where username specifies the name of the user's account for which you want to create or edit a crontab file. You can create your own crontab file without superuser privileges, but you must have superuser privileges to creating or edit a crontab file for root or another user.

    Caution – 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 would be overwritten with an empty file.

  2. Add command lines to the crontab file.

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

  3. Verify your crontab file changes.

    # crontab -l [username]

Example 8–1 Creating 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. Doing so ensures that the command executes properly.

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

ProcedureHow to Verify That a crontab File Exists

  1. 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 output shows that crontab files exist for users jones and smith.

    $ 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.