1CRONTAB(1) User Commands CRONTAB(1)
2
6 crontab - maintains crontab files for individual users
7
9 crontab [-u user] <file | ->
10 crontab [-T] <file | ->
11 crontab [-u user] <-l | -r | -e> [-i] [-s]
12 crontab -n [ hostname ]
13 crontab -c
14 crontab -V
15
17 Crontab is the program used to install a crontab table file, remove or
18 list the existing tables used to serve the cron(8) daemon. Each user
19 can have their own crontab, and though these are files in /var/spool/,
20 they are not intended to be edited directly. For SELinux in MLS mode,
21 you can define more crontabs for each range. For more information, see
22 selinux(8).
23 In this version of Cron it is possible to use a network-mounted shared
25 /var/spool/cron across a cluster of hosts and specify that only one of
26 the hosts should run the crontab jobs in the particular directory at
27 any one time. You may also use crontab from any of these hosts to edit
28 the same shared set of crontab files, and to set and query which host
29 should run the crontab jobs.
30 Scheduling cron jobs with crontab can be allowed or disallowed for dif‐
32 ferent users. For this purpose, use the cron.allow and cron.deny
33 files. If the cron.allow file exists, a user must be listed in it to
34 be allowed to use crontab. If the cron.allow file does not exist but
35 the cron.deny file does exist, then a user must not be listed in the
36 cron.deny file in order to use crontab. If neither of these files
37 exist, then only the super user is allowed to use crontab.
38 Another way to restrict the scheduling of cron jobs beyond crontab is
40 to use PAM authentication in /etc/security/access.conf to set up users,
41 which are allowed or disallowed to use crontab or modify system cron
42 jobs in the /etc/cron.d/ directory.
43 The temporary directory can be set in an environment variable. If it
45 is not set by the user, the /tmp directory is used.
46 When listing a crontab on a terminal the output will be colorized
48 unless an environment variable NO_COLOR is set.
49
51 -u Specifies the name of the user whose crontab is to be modified.
52 If this option is not used, crontab examines "your" crontab,
53 i.e., the crontab of the person executing the command. If no
54 crontab exists for a particular user, it is created for them the
55 first time the crontab -u command is used under their username.
56 -T Test the crontab file syntax without installing it. Once an
58 issue is found, the validation is interrupted, so this will not
59 return all the existing issues at the same execution.
60 -l Displays the current crontab on standard output.
62 -r Removes the current crontab.
64 -e Edits the current crontab using the editor specified by the VIS‐
66 UAL or EDITOR environment variables. After you exit from the
67 editor, the modified crontab will be installed automatically.
68 -i This option modifies the -r option to prompt the user for a
70 'y/Y' response before actually removing the crontab.
71 -s Appends the current SELinux security context string as an
73 MLS_LEVEL setting to the crontab file before editing / replace‐
74 ment occurs - see the documentation of MLS_LEVEL in crontab(5).
75 -n This option is relevant only if cron(8) was started with the -c
77 option, to enable clustering support. It is used to set the
78 host in the cluster which should run the jobs specified in the
79 crontab files in the /var/spool/cron directory. If a hostname
80 is supplied, the host whose hostname returned by gethostname(2)
81 matches the supplied hostname, will be selected to run the
82 selected cron jobs subsequently. If there is no host in the
83 cluster matching the supplied hostname, or you explicitly spec‐
84 ify an empty hostname, then the selected jobs will not be run at
85 all. If the hostname is omitted, the name of the local host
86 returned by gethostname(2) is used. Using this option has no
87 effect on the /etc/crontab file and the files in the /etc/cron.d
88 directory, which are always run, and considered host-specific.
89 For more information on clustering support, see cron(8).
90 -c This option is only relevant if cron(8) was started with the -c
92 option, to enable clustering support. It is used to query which
93 host in the cluster is currently set to run the jobs specified
94 in the crontab files in the directory /var/spool/cron , as set
95 using the -n option.
96 -V Print version and exit.
98
100 The files cron.allow and cron.deny cannot be used to restrict the exe‐
101 cution of cron jobs; they only restrict the use of crontab. In partic‐
102 ular, restricting access to crontab has no effect on an existing
103 crontab of a user. Its jobs will continue to be executed until the
104 crontab is removed.
105 The files cron.allow and cron.deny must be readable by the user invok‐
107 ing crontab. If this is not the case, then they are treated as non-
108 existent.
109
111 crontab(5), cron(8)
112
114 /etc/cron.allow
115 /etc/cron.deny
116
118 The crontab command conforms to IEEE Std1003.2-1992 (``POSIX'') with
119 one exception: For replacing the current crontab with data from stan‐
120 dard input the - has to be specified on the command line if the stan‐
121 dard input is a TTY. This new command syntax differs from previous
122 versions of Vixie Cron, as well as from the classic SVR3 syntax.
123
125 An informative usage message appears if you run a crontab with a faulty
126 command defined in it.
127
129 Paul Vixie ⟨vixie@isc.org⟩
130 Colin Dean ⟨colin@colin-dean.org⟩
131cronie 2019-10-29 CRONTAB(1)