cron/crontab/crontab.1

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.Dd December 20, 2016
.Dt CRONTAB 1
.Os
.Sh NAME
.Nm crontab
.Nd maintain crontab files for individual users (V3)
.Sh SYNOPSIS
.Nm
.Op Fl u Ar user
.Ar file
.Nm
.Op Fl u Ar user
{
.Fl l |
.Fl r Op Fl f
|
.Fl e
}
.Sh DESCRIPTION
The
.Nm
utility is the program used to install, deinstall or list the tables
used to drive the
.Xr cron 8
daemon in Vixie Cron.
Each user can have their own crontab, and though
these are files in
.Pa /var ,
they are not intended to be edited directly.
.Pp
If the
.Pa allow
file exists, then you must be listed therein in order to be allowed to use
this command.
If the
.Pa allow
file does not exist but the
.Pa deny
file does exist, then you must
.Em not
be listed in the
.Pa deny
file in order to use this command.
If neither of these files exists, then
depending on site-dependent configuration parameters, only the super user
will be allowed to use this command, or all users will be able to use this
command.
The format of these files is one username per line,
with no leading or trailing whitespace.
Lines of other formats will be ignored,
and so can be used for comments.
.Pp
The first form of this command is used to install a new crontab from some
named file or standard input if the pseudo-filename
.Sq Fl
is given.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl u
Specify the name of the user whose crontab is to be
tweaked.
If this option is not given,
.Nm
examines
.Dq your
crontab, i.e., the crontab of the person executing the
command.
Note that
.Xr su 1
can confuse
.Nm
and that if you are running inside of
.Xr su 1
you should always use the
.Fl u
option for safety's sake.
.It Fl l
Display the current crontab on standard output.
.It Fl r
Remove the current crontab.
By default the
.Fl r
option prompts for confirmation, adding the
.Fl f
option will attempt to remove the current crontab without confirmation.
.It Fl e
Edit the current crontab using the editor specified by
the
.Ev VISUAL
or
.Ev EDITOR
environment variables.
The specified editor
.Em must
edit the file in place;
any editor that unlinks the file and recreates it cannot be used.
After you exit
from the editor, the modified crontab will be installed automatically.
.El
.Sh FILES
.Bl -tag -width /var/cron/allow -compact
.It Pa /var/cron/allow
List of users allowed to use crontab
.It Pa /var/cron/deny
List of users prohibited from using crontab
.It Pa /var/cron/tabs
Directory for personal crontab files
.El
.Sh DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command
line.
.Sh SEE ALSO
.Xr crontab 5 ,
.Xr cron 8
.Sh STANDARDS
The
.Nm
command conforms to
.St -p1003.2
with the exception that the dangerous variant of calling
.Nm
without a file name in the first form of the command is not allowed by
this implementation.
The pseudo-filename
.Sq Fl
must be specified to read from standard input.
The new command syntax
differs from previous versions of Vixie Cron, as well as from the classic
SVR3 syntax.
.Sh AUTHORS
.An Paul Vixie Aq Mt paul@vix.com