{"id":2274,"date":"2015-09-17T19:27:40","date_gmt":"2015-09-17T18:27:40","guid":{"rendered":"https:\/\/stevepedwards.today\/DebianAdmin\/?p=2274"},"modified":"2015-09-17T19:27:40","modified_gmt":"2015-09-17T18:27:40","slug":"using-crontab-to-automate-commands-on-schedule-and-with-poweroff","status":"publish","type":"post","link":"https:\/\/stevepedwards.today\/DebianAdmin\/using-crontab-to-automate-commands-on-schedule-and-with-poweroff\/","title":{"rendered":"Using Crontab to Automate Commands on Schedule and with Poweroff"},"content":{"rendered":"
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man crontab<\/span><\/p>\n

crontab - maintain crontab files for individual users (Vixie Cron)<\/span><\/p>\n

SYNOPSIS<\/span><\/p>\n

crontab [ -u user ] file<\/span><\/p>\n

crontab [ -u user ] [ -i ] { -e | -l | -r }<\/span><\/p>\n

DESCRIPTION<\/span><\/p>\n

crontab is the program used to install, deinstall or list the tables<\/span><\/p>\n

used to drive the cron(8) daemon in Vixie Cron. Each user can have<\/span><\/p>\n

their own crontab, and though these are files in<\/span><\/p>\n

\/var\/spool\/cron\/crontabs, they are not intended to be edited directly.<\/span><\/p>\n

You may want to poweroff your PC automatically at the end of the day, or at a specific time, or run other commands like backups after hours etc. and crontab<\/b><\/span> can set this for you. <\/span><\/p>\n

It can be run by anyone depending on entries in the \/etc\/cron.allow or \/etc\/cron.deny if those files are created. <\/span><\/p>\n

Each user has their own file which is initially created using <\/span><\/p>\n

crontab -e<\/span><\/p>\n

This opens the default editor in Raspbian, but Mint gives a choice of editors, so for user root on the first file creation:<\/span><\/p>\n

root@AMDA8 \/home\/stevee $ crontab -e<\/span><\/span><\/p>\n

no crontab for test - using an empty one<\/span><\/p>\n

Select an editor. To change later, run 'select-editor'.<\/span><\/p>\n

1. \/bin\/ed<\/span><\/p>\n

2. \/bin\/nano <---- easiest<\/span><\/p>\n

3. \/usr\/bin\/vim.basic<\/span><\/p>\n

4. \/usr\/bin\/vim.tiny<\/span><\/p>\n

Choose 1-4 [2]:<\/span><\/p>\n

- and a command and time schedule is input under each column e.g:<\/span><\/p>\n

Once you choose your editor, or change it after with:<\/span><\/p>\n

select-editor<\/span><\/p>\n

you can add a cron job<\/span><\/p>\n

# Edit this file to introduce tasks to be run by cron.<\/span><\/p>\n

# <\/span><\/p>\n

# Each task to run has to be defined through a single line<\/span><\/p>\n

# indicating with different fields when the task will be run<\/span><\/p>\n

# and what command to run for the task<\/span><\/p>\n

# <\/span><\/p>\n

# To define the time you can provide concrete values for<\/span><\/p>\n

# minute (m), hour (h), day of month (dom), month (mon),<\/span><\/p>\n

# and day of week (dow) or use '*' in these fields (for 'any').# <\/span><\/p>\n

# Notice that tasks will be started based on the cron's system<\/span><\/p>\n

# daemon's notion of time and timezones.<\/span><\/p>\n

# <\/span><\/p>\n

# Output of the crontab jobs (including errors) is sent through<\/span><\/p>\n

# email to the user the crontab file belongs to (unless redirected).<\/span><\/p>\n

# <\/span><\/p>\n

# For example, you can run a backup of all your user accounts<\/span><\/p>\n

# at 5 a.m every week with:<\/span><\/p>\n

# 0 5 * * 1 tar -zcf \/var\/backups\/home.tgz \/home\/<\/span><\/p>\n

# <\/span><\/p>\n

# For more information see the manual pages of crontab(5) and cron(8)<\/span><\/p>\n

# <\/span><\/p>\n

# m h dom mon dow command<\/span><\/p>\n

00 17 * * * \/sbin\/poweroff<\/span><\/strong><\/p>\n

This means the \"poweroff\" command will run at 17:00 hrs every day of every month.<\/span><\/p>\n

Note my poweroff command uses the full path many googles about this people not being able to use \"shutdown\", \"poweroff\" or variants of these, which seem to need the full path (and be root), yet other commands like echo do not. I thought this was because of the $PATH variables for the user, but on checking, \/sbin IS in the root's\u00a0path anyway, so that 's not why this command fails to run on it's own in crontab:<\/span><\/p>\n

AMDA8 stevee # $PATH<\/span><\/span><\/p>\n

bash: \/usr\/local\/sbin:\/usr\/local\/bin:\/usr\/sbin:\/usr\/bin:\/sbin:<\/strong>\/bin:\/usr\/games:\/usr\/local\/games: No such file or directory<\/span><\/p>\n

I also thought this was maybe\u00a0due to currently running processes at a higher priority preventing cron running poweroff for safety\/continuity reasons, but even running:<\/span><\/p>\n

nice -n -20 poweroff <\/span><\/p>\n

which is the highest priority (-20 to +19) a command can run, it still did not run in crontab, as it needs a full path.<\/span><\/p>\n

The crontab file's headings respectively are:<\/span><\/p>\n

minutes (m) ; hours (h, 24hr) ; day of month (dom); month (mon); day of week (dow); command<\/span><\/strong><\/p>\n

Once entered, the file is saved using CtrlO using Raspian's cron editor's menu commands at the screen bottom, and exited with Ctrl X, or your own Mint editors usual commands vim say. This editor choice will be your default for any amendments later with crontab -e<\/b>.<\/span><\/p>\n

The file can be re-read and checked with :<\/span><\/p>\n

crontab -l<\/span><\/p>\n

The file is saved by default (in Raspbian and Mint) under the user's name in:<\/span><\/p>\n

ls -als \/var\/spool\/cron\/crontabs\/<\/span><\/p>\n

4 -rw------- 1 root crontab 1119 Sep 17 16:31 \/var\/spool\/cron\/crontabs\/root<\/b><\/span><\/p>\n

The user opens their own file, and as usual - root can view or change other's crontab files by specifying the username using:<\/span><\/p>\n

crontab -<\/span>e <\/span>-u<\/span> (username)<\/span><\/p>\n

Now it's just a matter of waiting until cron checks the clock and runs.<\/span><\/p>\n

Cron will mail the user with a report handy for debugging as in the poweroff command example above, as I got told that the file did not exist (i.e. the command) so cron just did not find poweroff.<\/span><\/p>\n

Run mail<\/span> to check if its installed if not, install and run it for local delivery only, following the screen prompts:<\/span><\/p>\n

test@AMDA8 \/home\/stevee $ mail<\/span><\/span><\/p>\n

The program 'mail' is currently not installed. To run 'mail' please ask your administrator to install the package 'mailutils'<\/span><\/p>\n

apt-get install mailutils<\/span><\/p>\n

\"\"Check cron is working with a simple test first set at least a minute or 2 in the future, as cron checks per minute to see if a job is spooled e.g:<\/p>\n

tty<\/span><\/p>\n

\/dev\/pts\/2<\/span><\/p>\n

crontab -e<\/span><\/p>\n

# m h dom mon dow command<\/span><\/p>\n

13 19 * * * date > \/dev\/pts\/2<\/span><\/p>\n

Hopefully, you get the output of the date command at the scheduled time, so cron works.<\/span><\/p>\n

AMDA8 stevee #<\/span> Thu Sep 17 19:13:01 BST 2015<\/span><\/p>\n

Now you can schedule those daily incremental backups with rsync - locally and remotely e.g.<\/span><\/p>\n

rsync -e ssh --progress \/home\/stevee\/* stevee@hpmint:\/home\/stevee\/ --exclude='Videos\/' --delete-excluded --exclude='.' -vahn<\/span><\/p>\n

Or to backup your home dir where the user folder has not been created yet on a local backup drive:<\/p>\n

rsync ~\/* \/media\/stevee\/982adb91-5828-4997-9c8c-c846c889b018\/stevee\/ --exclude='.' -vahn<\/span><\/p>\n

sending incremental file list<\/span>
\ncreated directory \/media\/stevee\/982adb91-5828-4997-9c8c-c846c889b018\/stevee<\/span>
\nContacts\/<\/span>
\nContacts\/Alex mot.vcf<\/span><\/p>\n

.....etc....<\/p>\n

ALWAYS dry-run (-n) any rsync command before you run it to prevent deletion errors. The above command creates a near mirror of my user's home directory excluding the .*cache etc files, and a large Video collection. Very useful.<\/p>\n

For a crontab line at 3pm, which you won't be watching so don't need --progress or -vhn; only -a to archive:<\/p>\n

0 15 * * *\u00a0rsync -e ssh \u00a0\/home\/stevee\/* stevee@hpmint:\/home\/stevee\/ --exclude='Videos\/' --delete-excluded --exclude='.' -a<\/span><\/p>\n

C<\/span>heck your mail<\/span> for the summary of the job - if mailutils is installed.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

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man crontab crontab - maintain crontab files for individual users (Vixie Cron) SYNOPSIS crontab [ -u user ] file crontab [ -u user ] [ -i ] { -e | -l | -r } DESCRIPTION crontab is the program used to install, deinstall or list the tables used to drive the cron(8) daemon in Vixie ...\u00a0 Using Crontab to Automate Commands on Schedule and with Poweroff<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-2274","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"a3_pvc":{"activated":true,"total_views":1,"today_views":0},"_links":{"self":[{"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/posts\/2274","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/comments?post=2274"}],"version-history":[{"count":0,"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/posts\/2274\/revisions"}],"wp:attachment":[{"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/media?parent=2274"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/categories?post=2274"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stevepedwards.today\/DebianAdmin\/wp-json\/wp\/v2\/tags?post=2274"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}