[deployment-guide/comm-rel: 68/727] modified Cron chapter
Jaromir Hradilek
jhradile at fedoraproject.org
Tue Oct 19 12:29:50 UTC 2010
commit 2b94245f3b3eacd9be6334c422874c47523487a6
Author: Martin Prpic <mprpic at redhat.com>
Date: Mon Jul 19 17:23:14 2010 +0200
modified Cron chapter
en-US/Automated_Tasks.xml | 259 ++++++++++++++++++++------------------------
1 files changed, 118 insertions(+), 141 deletions(-)
---
diff --git a/en-US/Automated_Tasks.xml b/en-US/Automated_Tasks.xml
index 10c5af6..f026e09 100644
--- a/en-US/Automated_Tasks.xml
+++ b/en-US/Automated_Tasks.xml
@@ -1,52 +1,40 @@
<?xml version='1.0'?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
]>
-<chapter
- id="ch-Automated_Tasks">
+<chapter id="ch-Automated_Tasks">
<title>Automated Tasks</title>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>Automated Tasks</primary>
</indexterm>
<para>In Linux, tasks, which are also known as <firstterm>jobs</firstterm>, can be configured to run automatically within a specified period of time, on a specified date, or when the system load average is below a specified number. &MAJOROS; is pre-configured to run important system tasks to keep the system updated. For example, the slocate database used by the <command>locate</command> command is updated daily. A system administrator can use automated tasks to perform periodic backups, monitor the system, run custom scripts, and more.</para>
<para>&MAJOROS; comes with several automated tasks utilities: <command>cron</command>, <command>at</command>, and <command>batch</command>.</para>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>Cron</primary>
</indexterm>
<section id="s1-autotasks-cron-anacron">
<title>Cron and Anacron</title>
<para>Both, Cron and Anacron, are daemons that can be used to schedule the execution of recurring tasks according to a combination of the time, day of the month, month, day of the week, and week.</para>
<para>Cron assumes that the system is on continuously. If the system is not on when a job is scheduled, it is not executed. Cron allows jobs to be run as often as every minute. Anacron does not assume the system is always on, remembers every scheduled job, and executes it the next time the system is up. However, Anacron can only run a job once a day.
- To schedule reccuring jobs, refer to <xref linkend="s2-configuring-tasks"/>. To schedule one-time jobs, refer to <xref
- linkend="s1-autotasks-at-batch"/>.</para>
- <para>To use the cron service, the <filename>cronie</filename> RPM package must be installed and the <command>crond</command> service must be running. Anacron is sub-package of cronie. To determine if these packages are installed, use the <command>rpm -q cronie cronie-anacron</command> command. </para>
- <section
- id="s2-autotasks-cron-service"
- lang="en-US,as-IN,bn-IN,gu-IN,hi-IN,kn-IN,ml-IN,mr-IN,or-IN,pa-IN,si-LK,ta-IN,te-IN">
+ To schedule reccurring jobs, refer to <xref linkend="s2-configuring-anacron-jobs"/> or <xref linkend="s2-configuring-cron-jobs"/>. To schedule one-time jobs, refer to <xref linkend="s1-autotasks-at-batch"/>.</para>
+ <para>To use the cron service, the <filename>cronie</filename> RPM package must be installed and the <command>crond</command> service must be running. <filename>anacron</filename> is a sub-package of <filename>cronie</filename>. To determine if these packages are installed, use the <command>rpm -q cronie cronie-anacron</command> command. </para>
+ <section id="s2-autotasks-cron-service" lang="en-US,as-IN,bn-IN,gu-IN,hi-IN,kn-IN,ml-IN,mr-IN,or-IN,pa-IN,si-LK,ta-IN,te-IN">
<title>Starting and Stopping the Service</title>
- <para>To determine if the service is running, use the command <command>/sbin/service crond status</command>. To start the cron service, use the command <command>/sbin/service crond start</command>. To stop the service, use the command <command>/sbin/service crond stop</command>. It is recommended that you start the service at boot time. Refer to <xref
- linkend="ch-Controlling_Access_to_Services"/> for details on starting the cron service automatically at boot time.</para>
+ <para>To determine if the service is running, use the command <command>/sbin/service crond status</command>. To start the cron service, use the command <command>/sbin/service crond start</command>. To stop the service, use the command <command>/sbin/service crond stop</command>. It is recommended that you start the service at boot time. Refer to <xref linkend="ch-Controlling_Access_to_Services"/> for details on starting the cron service automatically at boot time.</para>
</section>
- <section
- id="s2-configuring-tasks">
- <title>Configuring Tasks</title>
- <indexterm
- significance="normal">
+ <section id="s2-configuring-anacron-jobs">
+ <title>Configuring Anacron Jobs</title>
+ <indexterm significance="normal">
<primary>cron</primary>
<secondary>configuration file</secondary>
</indexterm>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>
<filename>crontab</filename>
</primary>
</indexterm>
-
- <section id="s3-configuring-anacron-jobs">
- <title>Configuring Anacron Jobs</title>
+
<para>The main configuration file to schedule jobs is <filename>/etc/anacrontab</filename>, which contains the following lines:</para>
-<screen>
+ <screen>
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
@@ -60,44 +48,44 @@ START_HOURS_RANGE=3-22
7 25 cron.weekly nice run-parts /etc/cron.weekly
@monthly 45 cron.monthly nice run-parts /etc/cron.monthly
</screen>
-<para>
+ <para>
The first three lines are variables used to configure the environment in which the anacron tasks are run. The <computeroutput>SHELL</computeroutput> variable tells the system which shell environment to use (in this example the bash shell). The <computeroutput>PATH</computeroutput> variable defines the path used to execute commands. The output of the anacron jobs are emailed to the username defined with the <computeroutput>MAILTO</computeroutput> variable. If the <computeroutput>MAILTO</computeroutput> variable is defined as an empty string (<computeroutput>MAILTO=""</computeroutput>), email is not sent.
</para>
-<para>
- The next two lines are variables that modify the time for each scheduled job. The <computeroutput>RANDOM_DELAY</computeroutput> variable denotes the maximum number of minutes that can randomly be added to the delay variable specified for each job. The minimum delay value is set, by default, to 6 minutes. A <computeroutput>RANDOM_DELAY</computeroutput> set to 12 would therefore add, randomly, between 6 and 12 minutes to the delay. <computeroutput>RANDOM_DELAY</computeroutput> can also be set to a value below 6, or even 0. When set to 0, no random delay is added. This proves to be useful when, for example, more computers that share one network connection need to download the same data every day. The <computeroutput>START_HOURS_RANGE</computeroutput> variable defines an interval (in hours) when scheduled jobs can be run. In case this time interval is missed, for example, due to a power down, then scheduled jobs are not executed that day.
+ <para>
+ The next two lines are variables that modify the time for each scheduled job. The <computeroutput>RANDOM_DELAY</computeroutput> variable denotes the maximum number of minutes that are be added to the <filename>delay in minutes</filename> variable which is specified for each job. The minimum delay value is set, by default, to 6 minutes. A <computeroutput>RANDOM_DELAY</computeroutput> set to 12 would therefore add, randomly, between 6 and 12 minutes to the <filename>delay in minutes</filename> for each jot in that particular anacrontab. <computeroutput>RANDOM_DELAY</computeroutput> can also be set to a value below 6, or even 0. When set to 0, no random delay is added. This proves to be useful when, for example, more computers that share one network connection need to download the same data every day. The <computeroutput>START_HOURS_RANGE</computeroutput> variable defines an interval (in hours) when scheduled jobs can be run. In case this time interval is missed, for example,
due to a power down, then scheduled jobs are not executed that day.
</para>
-<para>The rest of the lines in the <filename>/etc/anacrontab</filename> file represent scheduled jobs and have the following format:
+ <para>The rest of the lines in the <filename>/etc/anacrontab</filename> file represent scheduled jobs and have the following format:
</para>
-<screen>
+ <screen>
period in days delay in minutes job-identifier command
</screen>
-<itemizedlist>
- <listitem>
- <para>
- <computeroutput>period in days</computeroutput> - specifies the frequency of execution of the job in days. This variable can be represented by an integer or a macro (<computeroutput>@daily</computeroutput>, <computeroutput>@weekly</computeroutput>, <computeroutput>@monthly</computeroutput>), where <computeroutput>@daily</computeroutput> denotes the same value as the integer 1, <computeroutput>@weekly</computeroutput> the same as 7, and <computeroutput>@monthly</computeroutput> specifies that the job is run once a month, independent on the length of the month.
+ <itemizedlist>
+ <listitem>
+ <para>
+ <computeroutput>period in days</computeroutput> — specifies the frequency of execution of a job in days. This variable can be represented by an integer or a macro (<computeroutput>@daily</computeroutput>, <computeroutput>@weekly</computeroutput>, <computeroutput>@monthly</computeroutput>), where <computeroutput>@daily</computeroutput> denotes the same value as the integer 1, <computeroutput>@weekly</computeroutput> the same as 7, and <computeroutput>@monthly</computeroutput> specifies that the job is run once a month, independent on the length of the month.
</para>
- </listitem>
- <listitem>
- <para>
- <computeroutput>delay in minutes</computeroutput> - specifies the number of minutes anacron waits, if necessary, before executing a job. This variable is represented by an integer where 0 means no delay.
+ </listitem>
+ <listitem>
+ <para>
+ <computeroutput>delay in minutes</computeroutput> — specifies the number of minutes anacron waits, if necessary, before executing a job. This variable is represented by an integer where 0 means no delay.
</para>
- </listitem>
- <listitem>
- <para>
- <computeroutput>job-identifier</computeroutput> - specifies a unique name of a job which is used in the log files.
+ </listitem>
+ <listitem>
+ <para>
+ <computeroutput>job-identifier</computeroutput> — specifies a unique name of a job which is used in the log files.
</para>
- </listitem>
- <listitem>
- <para>
- <computeroutput>command</computeroutput> - specifies the command to execute. The command can either be a command such as <computeroutput>ls /proc >> /tmp/proc</computeroutput> or a command to execute a custom script.
+ </listitem>
+ <listitem>
+ <para>
+ <computeroutput>command</computeroutput> — specifies the command to execute. The command can either be a command such as <computeroutput>ls /proc >> /tmp/proc</computeroutput> or a command to execute a custom script.
</para>
- </listitem>
-</itemizedlist>
-<para>Any lines that begin with a hash mark (#) are comments and are not processed.</para>
-<section id="s4-anacron-examples">
- <title>Examples of Anacron Jobs </title>
- <para>The following example shows how a simple <filename>/etc/anacrontab</filename> file could look like:</para>
-<screen>
+ </listitem>
+ </itemizedlist>
+ <para>Any lines that begin with a hash mark (#) are comments and are not processed.</para>
+ <section id="s3-anacron-examples">
+ <title>Examples of Anacron Jobs </title>
+ <para>The following example shows a simple <filename>/etc/anacrontab</filename> file:</para>
+ <screen>
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
@@ -112,13 +100,19 @@ START_HOURS_RANGE=16-20
7 25 weeklyjob /etc/weeklyjob.bash
@monthly 45 monthlyjob ls /proc >> /tmp/proc
</screen>
+ <para>
+ All jobs defined in this <filename>anacrontab</filename> file are randomly delayed by 6-30 minutes and can be executed between 16:00 and 20:00. Thus, the first defined job will run anywhere between 16:26 and 16:50 every day. The command specified for this job will execute all present programs in the <filename>/etc/cron.daily</filename> directory (using the <command>run-parts</command> script which takes a directory as a command-line argument and sequentially executes every program within that directory). The second specified job will be executed once a week and will execute the <filename>weeklyjob.bash</filename> script in the <filename>/etc</filename> directory. The third job is executed once a month and runs a command to write the contents of the <filename>/proc</filename> to the <filename>/tmp/proc</filename> file (e.g. <computeroutput>ls /proc >> /tmp/proc</computeroutput>).
+</para>
+<section id="s3-disabling-anacron">
+<title>Disabling Anacron</title>
<para>
- All jobs defined in this <filename>anacrontab</filename> file are randomly delayed by 6-30 minutes and can be executed between 16:00 and 20:00. Thus, the first defined job will run anywhere between 16:26 and 16:50 every day. The command specified for this job will execute all present executables in the <filename>/etc/cron.daily</filename> directory (using the <command>run-parts</command> command). The second specified job will be executed once a week and will execute the <filename>weeklyjob.bash</filename> script in the <filename>/etc</filename> directory. The third job is executed once a month and runs a command to write the contents of the <filename>/proc</filename> to the <filename>/tmp/proc</filename> file (e.g. <computeroutput>ls /proc >> /tmp/proc</computeroutput>).
+ In case your system is continuously on and you do not require anacron to run your scheduled jobs, you can install the <filename>cronie-noanacron</filename> package which uninstalls the <filename>cronie-anacron</filename> package. Thus, you can define jobs using crontabs only.
</para>
</section>
-</section>
-<section id="s3-configuring-cron-jobs">
- <title>Configuring Cron Jobs</title>
+ </section>
+ </section>
+ <section id="s2-configuring-cron-jobs">
+ <title>Configuring Cron Jobs</title>
<!-- <indexterm
significance="normal">
<primary>cron</primary>
@@ -130,10 +124,10 @@ START_HOURS_RANGE=16-20
<filename>/var/spool/cron</filename>
</primary>
</indexterm> -->
- <para>
+ <para>
The configuration file to configure cron jobs, <filename>/etc/crontab</filename>, contains the following lines:
</para>
- <screen>
+ <screen>
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
@@ -148,16 +142,16 @@ HOME=/
# | | | | |
# * * * * * user command to be executed
</screen>
- <para>
- The first three lines contains the same variables as an anacrontab, <computeroutput>SHELL</computeroutput>, <computeroutput>PATH</computeroutput>, <computeroutput>MAILTO</computeroutput>. For more information about these variables, refer to <xref linkend="s3-configuring-anacron-jobs"/>. The fourth line contains the <computeroutput>HOME</computeroutput> variable. The <computeroutput>HOME</computeroutput> variable can be used to set the home directory to use when executing commands or scripts.
+ <para>
+ The first three lines contain the same variables as an <filename>anacrontab</filename> file, <computeroutput>SHELL</computeroutput>, <computeroutput>PATH</computeroutput> and <computeroutput>MAILTO</computeroutput>. For more information about these variables, refer to <xref linkend="s2-configuring-anacron-jobs"/>. The fourth line contains the <computeroutput>HOME</computeroutput> variable. The <computeroutput>HOME</computeroutput> variable can be used to set the home directory to use when executing commands or scripts.
</para>
- <para>
+ <para>
The rest of the lines in the <filename>/etc/crontab</filename> file represent scheduled jobs and have the following format:
</para>
- <screen>
+ <screen>
minute hour day month day of week user command
</screen>
- <itemizedlist>
+ <itemizedlist>
<listitem>
<para>
<computeroutput>minute</computeroutput> — any integer from 0 to 59</para>
@@ -176,11 +170,11 @@ minute hour day month day of week user command
</listitem>
<listitem>
<para>
- <computeroutput>dayofweek</computeroutput> — any integer from 0 to 7, where 0 or 7 represents Sunday (or the short name of the week such as sun or mon)</para>
+ <computeroutput>day of week</computeroutput> — any integer from 0 to 7, where 0 or 7 represents Sunday (or the short name of the week such as sun or mon)</para>
</listitem>
<listitem>
<para>
- <computeroutput>user</computeroutput> —
+ <computeroutput>user</computeroutput> — specifies the user under which the jobs are run
</para>
</listitem>
<listitem>
@@ -193,65 +187,62 @@ minute hour day month day of week user command
<para>A list of values separated by commas (,) specifies a list. For example, <userinput>3, 4, 6, 8</userinput> indicates those four specific integers.</para>
<para>The forward slash (/) can be used to specify step values. The value of an integer can be skipped within a range by following the range with <userinput>/<<replaceable>integer</replaceable>></userinput>. For example, <userinput>0-59/2</userinput> can be used to define every other minute in the minute field. Step values can also be used with an asterisk. For instance, the value <userinput>*/3</userinput> can be used in the month field to run the task every third month.</para>
<para>Any lines that begin with a hash mark (#) are comments and are not processed.</para>
- <para>Users other than root can configure cron tasks by using the <command>crontab</command> utility. All user-defined crontabs are stored in the <filename>/var/spool/cron/</filename> directory and are executed using the usernames of the users that created them. To create a crontab as a user, login as that user and type the command <command>crontab -e</command> to edit the user's crontab using the editor specified by the <computeroutput>VISUAL</computeroutput> or <computeroutput>EDITOR</computeroutput> environment variable. The file uses the same format as <filename>/etc/crontab</filename>. When the changes to the crontab are saved, the crontab is stored according to username and written to the file <filename>/var/spool/cron/<replaceable>username</replaceable></filename>.</para>
+ <para>Users other than root can configure cron tasks by using the <command>crontab</command> utility. All user-defined crontabs are stored in the <filename>/var/spool/cron/</filename> directory and are executed using the usernames of the users that created them. To create a crontab as a user, login as that user and type the command <command>crontab -e</command> to edit the user's crontab using the editor specified by the <computeroutput>VISUAL</computeroutput> or <computeroutput>EDITOR</computeroutput> environment variable. The file uses the same format as <filename>/etc/crontab</filename>. When the changes to the crontab are saved, the crontab is stored according to username and written to the file <filename>/var/spool/cron/<replaceable>username</replaceable>
+ </filename>. To list the contents of your own personal crontab file, use the <command>crontab -l</command> command. </para>
<note>
<title>Note</title>
- <para>
+ <para>
When using the <command>crontab</command> utility, there is no need to specify a user when defining a job.
</para>
</note>
-
- <!-- CRON.D -->
- <para>TBD: If a cron task is required to be executed on a schedule other than hourly, daily, weekly, or monthly, it can be added to the <filename>/etc/cron.d/</filename> directory. All files in this directory use the same syntax as <filename>/etc/crontab</filename>.</para>
-
-
-
- <para>The cron daemon checks the <filename>/etc/crontab</filename> file, the <filename>/etc/cron.d/</filename> directory, and the <filename>/var/spool/cron/</filename> directory every minute for any changes. If any changes are found, they are loaded into memory. Thus, the daemon does not need to be restarted if a crontab file is changed.</para>
-</section>
-<section
- id="s3-autotasks-cron-access">
+ <para>The <filename>/etc/cron.d/</filename> directory contains files that have the same syntax as the <filename>/etc/crontab</filename> file. Only root is allowed to create and modify files in this directory</para>
+ <note>
+ <title>Note</title>
+ <para>The cron daemon checks the <filename>/etc/anacrontab</filename> file, the <filename>/etc/crontab</filename> file, the <filename>/etc/cron.d/</filename> directory, and the <filename>/var/spool/cron/</filename> directory every minute for any changes. If any changes are found, they are loaded into memory. Thus, the daemon does not need to be restarted if an anacrontab or a crontab file is changed.</para>
+ </note>
+ </section>
+ <section id="s2-autotasks-cron-access">
<title>Controlling Access to Cron</title>
<para>The <filename>/etc/cron.allow</filename> and <filename>/etc/cron.deny</filename> files are used to restrict access to cron. The format of both access control files is one username on each line. Whitespace is not permitted in either file. The cron daemon (<command>crond</command>) does not have to be restarted if the access control files are modified. The access control files are read each time a user tries to add or delete a cron task.</para>
<para>The root user can always use cron, regardless of the usernames listed in the access control files.</para>
<para>If the file <filename>cron.allow</filename> exists, only users listed in it are allowed to use cron, and the <filename>cron.deny</filename> file is ignored.</para>
<para>If <filename>cron.allow</filename> does not exist, users listed in <filename>cron.deny</filename> are not allowed to use cron.</para>
- <para>Access can also be controlled through Pluggable authentication modules (PAM). These settings are stored in <filename>/etc/security/access.conf</filename>. For example, adding the following line in this file forbids creating crontabs for all other users than root:
+ <para>Access can also be controlled through Pluggable Authentication Modules (PAM). These settings are stored in <filename>/etc/security/access.conf</filename>. For example, adding the following line in this file forbids creating crontabs for all users except the root user:
</para>
-<screen>
+ <screen>
-:ALL EXCEPT root :cron
</screen>
<para>
- The forbidden jobs will be logged in an appropriate log file or, when using “crontab -e”, returned to the standard output. For more information, refer to <filename>access.conf.5</filename>.
+ The forbidden jobs will be logged in an appropriate log file or, when using “crontab -e”, returned to the standard output. For more information, refer to <filename>access.conf.5</filename> (i.e. <command>man 5 access.conf</command>).
</para>
</section>
-<section id="s3-black-white-listing-of-cron-jobs">
- <title>Black/White Listing of Cron Jobs</title>
- <para>
- Black/White listing of jobs is used to omit parts of the defined jobs that do not need to be executed. When running the <command>run-parts</command> command on a cron folder, such as <filename>/etc/cron.daily</filename>, we can define which of the executables in this folder will not be executed by the <command>run-parts</command> command. To define a black list, create a <filename>jobs.deny</filename> file in the folder that <command>run-parts</command> will be executing from. For example, if we need to omit a particular executable from /etc/cron.daily, then, a file <filename>/etc/cron.daily/jobs.deny</filename> has to be created. In this file, specify the names of the omitted executables from the same directory. These will not be executed when a command, such as <computeroutput>run-parts /etc/cron.daily</computeroutput>, is executed by a specific job. To define a white list, create a <filename>jobs.allow</filename> file. The principles of <filename>jobs.deny</filename>
and <filename>jobs.allow</filename> are the same as those of <filename>cron.deny</filename> and <filename>cron.allow</filename> described in section <xref linkend="s3-autotasks-cron-access"/>.
- </para>
- </section>
- </section>
+ <section id="s2-black-white-listing-of-cron-jobs">
+ <title>Black/White Listing of Cron Jobs</title>
+ <para>
+ Black/White listing of jobs is used to omit parts of the defined jobs that do not need to be executed. When calling the <command>run-parts</command> script on a cron folder, such as <filename>/etc/cron.daily</filename>, we can define which of the programs in this folder will not be executed by <command>run-parts</command>.
+ </para>
+ <para>To define a black list, create a <filename>jobs.deny</filename> file in the folder that <command>run-parts</command> will be executing from. For example, if we need to omit a particular program from /etc/cron.daily, then, a file <filename>/etc/cron.daily/jobs.deny</filename> has to be created. In this file, specify the names of the omitted programs from the same directory. These will not be executed when a command, such as <computeroutput>run-parts /etc/cron.daily</computeroutput>, is executed by a specific job.</para>
+ <para>To define a white list, create a <filename>jobs.allow</filename> file.</para>
+ <para>
+ The principles of <filename>jobs.deny</filename> and <filename>jobs.allow</filename> are the same as those of <filename>cron.deny</filename> and <filename>cron.allow</filename> described in section <xref linkend="s2-autotasks-cron-access"/>.
+ </para>
+ </section>
</section>
-
- <section
- id="s1-autotasks-at-batch">
+ <section id="s1-autotasks-at-batch">
<title>At and Batch</title>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>
<command>at</command>
</primary>
</indexterm>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>
<command>batch</command>
</primary>
</indexterm>
<para>While cron is used to schedule recurring tasks, the <command>at</command> command is used to schedule a one-time task at a specific time and the <command>batch</command> command is used to schedule a one-time task to be executed when the systems load average drops below 0.8.</para>
<para>To use <command>at</command> or <command>batch</command>, the <filename>at</filename> RPM package must be installed, and the <command>atd</command> service must be running. To determine if the package is installed, use the <command>rpm -q at</command> command. To determine if the service is running, use the command <command>/sbin/service atd status</command>.</para>
- <section
- id="s2-autotasks-at-configuring">
+ <section id="s2-autotasks-at-configuring">
<title>Configuring At Jobs</title>
<para>To schedule a one-time job at a specific time, type the command <command>at <replaceable>time</replaceable>
</command>, where <command><replaceable>time</replaceable>
@@ -289,13 +280,10 @@ minute hour day month day of week user command
<keycap>D</keycap>
</keycombo> on a blank line to exit. If a script is entered, the shell used is the shell set in the user's <envar>SHELL</envar> environment, the user's login shell, or <command>/bin/sh</command> (whichever is found first).</para>
<para>If the set of commands or script tries to display information to standard out, the output is emailed to the user.</para>
- <para>Use the command <command>atq</command> to view pending jobs. Refer to <xref
- linkend="s2-autotasks-at-batch-viewing"/> for more information.</para>
- <para>Usage of the <command>at</command> command can be restricted. For more information, refer to <xref
- linkend="s2-autotasks-at-batch-controlling-access"/> for details.</para>
+ <para>Use the command <command>atq</command> to view pending jobs. Refer to <xref linkend="s2-autotasks-at-batch-viewing"/> for more information.</para>
+ <para>Usage of the <command>at</command> command can be restricted. For more information, refer to <xref linkend="s2-autotasks-at-batch-controlling-access"/> for details.</para>
</section>
- <section
- id="s2-autotasks-batch-configuring">
+ <section id="s2-autotasks-batch-configuring">
<title>Configuring Batch Jobs</title>
<para>To execute a one-time task when the load average is below 0.8, use the <command>batch</command> command.</para>
<para>After typing the <command>batch</command> command, the <prompt>at></prompt> prompt is displayed. Type the command to execute, press <keycap>Enter</keycap>, and type <keycombo><keycap>Ctrl</keycap>
@@ -306,34 +294,22 @@ minute hour day month day of week user command
<keycap>D</keycap>
</keycombo> on a blank line to exit. If a script is entered, the shell used is the shell set in the user's <envar>SHELL</envar> environment, the user's login shell, or <command>/bin/sh</command> (whichever is found first). As soon as the load average is below 0.8, the set of commands or script is executed.</para>
<para>If the set of commands or script tries to display information to standard out, the output is emailed to the user.</para>
- <para>Use the command <command>atq</command> to view pending jobs. Refer to <xref
- linkend="s2-autotasks-at-batch-viewing"/> for more information.</para>
- <para>Usage of the <command>batch</command> command can be restricted. For more information, refer to <xref
- linkend="s2-autotasks-at-batch-controlling-access"/> for details.</para>
+ <para>Use the command <command>atq</command> to view pending jobs. Refer to <xref linkend="s2-autotasks-at-batch-viewing"/> for more information.</para>
+ <para>Usage of the <command>batch</command> command can be restricted. For more information, refer to <xref linkend="s2-autotasks-at-batch-controlling-access"/> for details.</para>
</section>
- <section
- id="s2-autotasks-at-batch-viewing">
+ <section id="s2-autotasks-at-batch-viewing">
<title>Viewing Pending Jobs</title>
<para>To view pending <command>at</command> and <command>batch</command> jobs, use the <command>atq</command> command. The <command>atq</command> command displays a list of pending jobs, with each job on a line. Each line follows the job number, date, hour, job class, and username format. Users can only view their own jobs. If the root user executes the <command>atq</command> command, all jobs for all users are displayed.</para>
</section>
- <section
- id="s2-autotasks-commandline-options">
+ <section id="s2-autotasks-commandline-options">
<title>Additional Command Line Options</title>
<para>Additional command line options for <command>at</command> and <command>batch</command> include:</para>
- <table
- id="tb-at-command-line-options">
+ <table id="tb-at-command-line-options">
<title>
<command>at</command> and <command>batch</command> Command Line Options</title>
- <tgroup
- cols="2">
- <colspec
- colname="option"
- colnum="1"
- colwidth="20*"/>
- <colspec
- colname="description"
- colnum="2"
- colwidth="50*"/>
+ <tgroup cols="2">
+ <colspec colname="option" colnum="1" colwidth="20*"/>
+ <colspec colname="description" colnum="2" colwidth="50*"/>
<thead>
<row>
<entry>
@@ -373,48 +349,39 @@ minute hour day month day of week user command
</tgroup>
</table>
</section>
- <section
- id="s2-autotasks-at-batch-controlling-access">
+ <section id="s2-autotasks-at-batch-controlling-access">
<title>Controlling Access to At and Batch</title>
<para>The <filename>/etc/at.allow</filename> and <filename>/etc/at.deny</filename> files can be used to restrict access to the <command>at</command> and <command>batch</command> commands. The format of both access control files is one username on each line. Whitespace is not permitted in either file. The <command>at</command> daemon (<command>atd</command>) does not have to be restarted if the access control files are modified. The access control files are read each time a user tries to execute the <command>at</command> or <command>batch</command> commands.</para>
<para>The root user can always execute <command>at</command> and <command>batch</command> commands, regardless of the access control files.</para>
<para>If the file <filename>at.allow</filename> exists, only users listed in it are allowed to use <command>at</command> or <command>batch</command>, and the <filename>at.deny</filename> file is ignored.</para>
<para>If <filename>at.allow</filename> does not exist, users listed in <filename>at.deny</filename> are not allowed to use <command>at</command> or <command>batch</command>.</para>
</section>
- <section
- id="s2-autotasks-at-batch-service"
- lang="en-US,as-IN,bn-IN,gu-IN,hi-IN,kn-IN,ml-IN,mr-IN,or-IN,pa-IN,si-LK,ta-IN,te-IN">
+ <section id="s2-autotasks-at-batch-service" lang="en-US,as-IN,bn-IN,gu-IN,hi-IN,kn-IN,ml-IN,mr-IN,or-IN,pa-IN,si-LK,ta-IN,te-IN">
<title>Starting and Stopping the Service</title>
- <para>To start the <command>at</command> service, use the command <command>/sbin/service atd start</command>. To stop the service, use the command <command>/sbin/service atd stop</command>. It is recommended that you start the service at boot time. Refer to <xref
- linkend="ch-Controlling_Access_to_Services"/> for details on starting the cron service automatically at boot time.</para>
+ <para>To start the <command>at</command> service, use the command <command>/sbin/service atd start</command>. To stop the service, use the command <command>/sbin/service atd stop</command>. It is recommended that you start the service at boot time. Refer to <xref linkend="ch-Controlling_Access_to_Services"/> for details on starting the cron service automatically at boot time.</para>
</section>
</section>
- <section
- id="s1-autotasks-additional-resources">
+ <section id="s1-autotasks-additional-resources">
<title>Additional Resources</title>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>cron</primary>
<secondary>additional resources</secondary>
</indexterm>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>at</primary>
<secondary>additional resources</secondary>
</indexterm>
- <indexterm
- significance="normal">
+ <indexterm significance="normal">
<primary>batch</primary>
<secondary>additional resources</secondary>
</indexterm>
<para>To learn more about configuring automated tasks, refer to the following resources.</para>
- <section
- id="s2-autotasks-installed-docs">
+ <section id="s2-autotasks-installed-docs">
<title>Installed Documentation</title>
<itemizedlist>
<listitem>
<para>
- <filename>cron</filename> man page — overview of cron.</para>
+ <filename>cron</filename> man page — contains an overview of cron.</para>
</listitem>
<listitem>
<para>
@@ -422,6 +389,16 @@ minute hour day month day of week user command
</listitem>
<listitem>
<para>
+ <filename>anacron</filename> man page — contains an overview of anacron.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <filename>anacrontab</filename> man page — contains an overview of the <filename>anacrontab</filename> file.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
<filename>/usr/share/doc/at-<replaceable><version></replaceable>/timespec</filename> contains more detailed information about the times that can be specified for cron jobs.</para>
</listitem>
<listitem>
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