anacron

anacron is a computer program that performs periodic command scheduling, which is traditionally done by cron, but without assuming that the system is running continuously. Thus, it can be used to control the execution of daily, weekly, and monthly jobs (or anything with a period of n days) on systems that don't run 24 hours a day. anacron was originally conceived and implemented by Christian Schwarz in Perl, for the Unix operating system. The current implementation, in C, was written by Itai Tzur and is actively maintained by Sean 'Shaleh' Perry.

Advantages

Unix systems commonly run "housekeeping chores" such as log rotation, unused files deletion, indexing local files for the search engine, sending disk usage reports, etc. A program called cron may be used to schedule these tasks.

With cron, tasks are commonly scheduled to be executed when the system is expected to be idle. If the system is off at the moment a task should be run, it will not be executed. Anacron is different and moves tasks to different moments so they are run when the system is on and utilising cron.

Disadvantages

Only the system administrator can configure anacron tasks. In contrast, cron allows non-admin users to configure scheduled tasks. If necessary, a non-admin user can use the at Unix command to request a scheduled task (which is guaranteed to run). Upon starting, this command can then automatically request to run itself at a future date, thus giving the appearance of a regularly scheduled task, with guaranteed execution.

anacron can run tasks only once a day (or less often such as weekly or monthly). In contrast, cron allows tasks to run as often as every minute (but does not guarantee their execution if the system goes down). In practice, this is not usually an issue, since it is rare to have a task that must be guaranteed to run more often than (at least) once a day — especially on a system that is not necessarily running at all times.

If the system is rebooted or started after midnight, the daily tasks are run after a user-specified delay in synchronized fashion (sequential order), so only one anacron-task is running at a time. When that task is finished, the next one starts and so on.

This behaviour can be overridden to allow concurrent (parallel) tasks, but can consume system resources that are needed by the user to do work. In contrast, cron will only run daily tasks at the time set (e.g. in the middle of the night, when presumably the machine is not being used).

fcron is another implementation of cron, which attempts to fulfill the roles of both Vixiecron and anacron.

External links

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix commands

This article is issued from Wikipedia - version of the 6/13/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.

anacron

Advantages

Disadvantages

See also

External links