daemon to execute scheduled commands (Vixie
utility should be started from
. It will return immediately,
so you do not need to start it with '&'.
for crontab files which are
named after accounts in /etc/passwd
crontabs found are loaded into memory. The
utility also searches for
and files in
which are in a
different format (see
utility then wakes up every minute,
examining all stored crontabs, checking each command to see if it should be
run in the current minute. Before running a command from a per-account crontab
checks the status of the account
and skips the command if the account is unavailable, e.g., locked out or
expired. Commands from /etc/crontab
this check. When executing commands, any output is mailed to the owner of the
crontab (or to the user named in the
environment variable in the crontab, if such exists).
checks each minute to see
if its spool directory's modification time (or the modification time on
) has changed, and if it has,
will then examine the modification
time on all crontabs and reload those which have changed. Thus
need not be restarted whenever a
crontab file is modified. Note that the
command updates the modification time of the spool directory whenever it
changes a crontab.
- Enable time jitter. Prior to executing commands,
cron will sleep a random number of
seconds in the range from 0 to jitter.
This will not affect superuser jobs (see
-J). A value for
jitter must be between 0 and 60
inclusive. Default is 0, which effectively disables time jitter.
This option can help to smooth down system load spikes during moments when a
lot of jobs are likely to start at once, e.g., at the beginning of the
first minute of each hour.
- Enable time jitter for superuser jobs. The same as
-j except that it will affect jobs run
by the superuser only.
- Overrides the default recipient for
cron mail. Each
MAILTO explicitly set will send
mail to the mailto mailbox. Sending mail
will be disabled by default if mailto set
to a null string, usually specified in a shell as
- Do not daemonize; run in foreground instead.
- Enable special handling of situations when the GMT offset of the local
timezone changes, such as the switches between the standard time and
daylight saving time.
The jobs run during the GMT offset changes time as intuitively expected. If
a job falls into a time interval that disappears (for example, during the
switch from standard time) to daylight saving time or is duplicated (for
example, during the reverse switch), then it is handled in one of two
The first case is for the jobs that run every at hour of a time interval
overlapping with the disappearing or duplicated interval. In other words,
if the job had run within one hour before the GMT offset change (and cron
was not restarted nor the
changed after that) or would run after the change at the next hour. They
work as always, skip the skipped time or run in the added time as usual.
The second case is for the jobs that run less frequently. They are executed
exactly once, they are not skipped nor executed twice (unless cron is
restarted or the user's
is changed during such a time interval). If an interval disappears due to
the GMT offset change, such jobs are executed at the same absolute point
of time as they would be in the old time zone. For example, if exactly one
hour disappears, this point would be during the next hour at the first
minute that is specified for them in
- Disable the special handling of situations when the GMT offset of the
local timezone changes, to be compatible with the old (default) behavior.
If both options
-s are specified, the option specified
- Enable writing of debugging information to standard output. One or more of
the following comma separated debugflag
identifiers must be specified:
- currently not used
- make the other debug flags more verbose
- be verbose when loading crontab files
- be verbose about miscellaneous one-off events
- be verbose about parsing individual crontab lines
- be verbose about the state of the process, including all of its
- be verbose when iterating through the scheduling algorithms
- trace through the execution, but do not perform any actions
- System crontab file
- Directory for optional/modularized system crontab files.
configuration file for
- Directory for third-party package provided crontab files.
- Directory for personal crontab files