cron(8) System Manager's Manual cron(8)NAME
cron - The system clock daemon
The cron daemon runs shell commands at specified dates and times. Commands that are to run according to a regular or periodic schedule are
found within the crontab files. Commands that are to run once only are found within the at files. You submit crontab and at file entries
by using the crontab and at commands. Because the cron process exits only when killed or when the system stops, only one cron daemon
should exist on the system at any given time. Normally, you start the cron daemon from within a run command file.
During process initialization and when cron detects a change, it examines the crontab and at files. This strategy reduces the overhead of
checking for new or changed files at regularly scheduled intervals. The cron command creates a log of its activities. The cron daemon
must be started from the system startup scripts because it must begin execution without a login user ID set. The cron daemon starts each
job with the following process attributes stored with the job by the invoking process: Login user ID Effective and real user IDs Effective
and real group IDs Supplementary groups
It also establishes the following attributes from the authentication profile of the account associated with the login user ID of the invok-
ing process: Audit control and disposition masks Kernel authorizations
The at and batch programs will refuse to accept jobs submitted from processes whose login user ID is different from the real user ID.
Specifies the command path. Main cron directory Directory containing the crontab files. List of allowed users. List of denied users His-
tory information for cron Queue description file for at, batch, and cron
Commands: at(1), crontab(1), rc0(8), rc2(8), rc3(8)
Files: queuedefs(4) delim off
Check Out this Related Man Page
cron(1M) System Administration Commands cron(1M)NAME
cron - clock daemon
cron starts a process that executes commands at specified dates and times.
You can specify regularly scheduled commands to cron according to instructions found in crontab files in the directory
/var/spool/cron/crontabs. Users can submit their own crontab file using the crontab(1) command. Commands which are to be executed only once
can be submitted using the at(1) command.
cron only examines crontab or at command files during its own process initialization phase and when the crontab or at command is run. This
reduces the overhead of checking for new or changed files at regularly scheduled intervals.
As cron never exits, it should be executed only once. This is done routinely by way of the svc:/system/cron:default service. The file
/etc/cron.d/FIFO file is used as a lock file to prevent the execution of more than one instance of cron.
cron captures the output of the job's stdout and stderr streams, and, if it is not empty, mails the output to the user. If the job does not
produce output, no mail is sent to the user. An exception is if the job is an at(1) job and the -m option was specified when the job was
cron and at jobs are not executed if your account is locked. Jobs and processses execute. The shadow(4) file defines which accounts are not
locked and will have their jobs and processes executed.
Setting cron Jobs Across Timezones
The timezone of the cron daemon sets the system-wide timezone for cron entries. This, in turn, is by set by default system-wide using
If some form of daylight savings or summer/winter time is in effect, then jobs scheduled during the switchover period could be executed
once, twice, or not at all.
Setting cron Defaults
To keep a log of all actions taken by cron, you must specify CRONLOG=YES in the /etc/default/cron file. If you specify CRONLOG=NO, no log-
ging is done. Keeping the log is a user configurable option since cron usually creates huge log files.
You can specify the PATH for user cron jobs by using PATH= in /etc/default/cron. You can set the PATH for root cron jobs using SUPATH= in
/etc/default/cron. Carefully consider the security implications of setting PATH and SUPATH.
Example /etc/default/cron file:
This example enables logging and sets the default PATH used by non-root jobs to /usr/bin:/usr/ucb:. Root jobs continue to use
The cron log file is periodically rotated by logadm(1M).
/etc/cron.d Main cron directory
/etc/cron.d/FIFO Lock file
/etc/default/cron cron default settings file
/var/cron/log cron history information
/var/spool/cron Spool area
/etc/cron.d/queuedefs Queue description file for at, batch, and cron
/etc/logadm.conf Configuration file for logadm
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Availability |SUNWcsu |
SEE ALSO svcs(1), at(1), crontab(1), sh(1), logadm(1M), svcadm(1M), queuedefs(4), shadow(4), attributes(5), smf(5)NOTES
The cron service is managed by the service management facility, smf(5), under the service identifier:
Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using svcadm(1M). The ser-
vice's status can be queried using the svcs(1) command.
A history of all actions taken by cron is stored in /var/cron/log and possibly in /var/cron/olog.
SunOS 5.10 5 Aug 2004 cron(1M)