COHERENT manpages
This page displays the COHERENT manpage for crontab [Copy a command file into the crontab directory].
List of available manpages
Index
crontab -- Command Copy a command file into the crontab directory /usr/bin/crontab [-l] [-r] [-f filename] [-m[ed]] [-uuser] The command crontab copies a command file into directory /usr/spool/cron/crontabs. This directory holds the command files for all users. This mechanism permits each user to have her own file of commands to be executed periodically. If the file name is `-', then crontab reads the standard input. crontab recognizes the following options. -f filename Replace your crontab file with filename. -l List your crontab file. -m[ed] Enable/disable the sending of mail to a user about any command in her crontab file that fails. -r Remove your crontab file. -u user Specify user. Only the superuser root can specify any user other than herself. Allowing and Denying Access The files /usr/lib/cron/cron.allow and /usr/lib/cron/cron.deny let the system administrator govern which users can use the crontab command: -> If cron.allow exists, then crontab checks its contents; if a given user is identified therein, then she can use crontab. Obviously, if cron.allow exists but is empty, then nobody can use crontab. -> If cron.allow does not exist, then crontab checks the contents of cron.deny. If a given user is identified therein, then she cannot use crontab; otherwise, she can. If cron.allow does not exist and cron.deny exists but is empty, then everyone can use crontab. -> If neither file exists, then everyone can use crontab. Format of a crontab File A crontab command file consists of lines separated by newlines. Each line consists of six fields separated by white space (tabs or blanks). The first five fields describe the scheduled execution time of the command. Respectively, they represent the minute (0-59), hour (0-23), day of the month (1-31), month of the year (1-12), and day of the week (0-6, 0 indicates Sunday). Each field can contain a single integer in the appropriate range, a pair of integers separated by a hyphen `-' (meaning all integers between the two, inclusive), an asterisk `*' (meaning all legal values), or a comma-separated list of the above forms. The remainder of the line gives the command to be executed at the given time. For example, the crontab entry 29 * * 7 0 msg henry Succotash! means that every hour on the half-hour during each Sunday in July, cron will invoke the command msg, and the user named henry will have the message daemon: Succotash! written on his terminal's screen (if he is logged in). crond recognizes three special characters and escape sequences in a crontab file. If a command contains the percent character `%', crond executes only the portion up to the first `%' as a command, then passes the remainder to the command as its standard input. crond translates any percent characters `%' in the remainder to newlines. To prevent the special interpretation of a `%', precede it with a backslash, `\%'. Finally, crond removes the sequence \<newline> from the text before it passes the text to the shell sh; this can be used to make an entry in the crontab more legible. You must pay special attention to permissions when you write a crontab command file. For information on how the crontab daemon crond manipulates permissions, see the entry for crond in the Lexicon. Directories and Files /usr/spool/cron/crontabs Main cron directory. It holds each user's command file. Permissions: 700 root root. /usr/lib/cron/FIFO Lock file (named pipe). Created by cron; removed by crond/rc. /usr/lib/cron/cron.allow List of allowed users. Permissions: 600 root root. /usr/lib/cron/cron.deny List of denied users. Permissions: 600 root root. /usr/lib/crontab Global crontab file, used by previous COHERENT cron mechanism. /usr/spool/cron Spool directory parent. Permissions: 700 root root. /usr/spool/cron/crontabs Spool directory. Permissions: 700 root root. See Also commands cron Notes COHERENT crontab is superset of the command of the same name included with UNIX System V release 3 (SVR3). The main differences are as follows: -> COHERENT crontab prints the usage when no options have been chosen, whereas SVR3 crontab reads stdin and can just remove the user's crontab file. -> SVR3 crontab does not include option -f file_name. -> SVR3 crontab does not include option -u user. Under SVR3 crontab, you must su to another user (e.g., uucp) before you can maintain her crontab file.