Cron is a job scheduler that allows users to run commands periodically.

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Interactive shell with environment identical to cron

I am aware of a lot of pitfalls in the magic world of crontabs, but sometimes it would help troubleshooting a lot when you have some smart way to enter an interactive (bash) shell with exact identical ...
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Run script in a non interactive shell?

I have a cron job that is running a script. When I run the script via an interactive shell (ssh'ed to bash) it works fine. When the script runs by itself via cron it fails. My guess is that it is ...
9
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1answer
449 views

Finding which cron jobs are scheduled to run at some future date/time X

Is there a way to "query" a crontab to find which cron jobs run at some arbitrary date/time, or during a certain range of times? For example, determine which will be run at sometime between 14:00 and ...
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0answers
102 views

Cron vs systemd timers

[NOTE: The intent of this question is to help people evaluate whether systemd timers would be a good choice for their job timing needs. Many (most?) people are probably using cron, but maybe some are ...
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3answers
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Run multiple cron jobs where one job takes a long time

I have the following general question regarding cron jobs. Suppose I have the following in my crontab: * 10 * * * * someScript.sh * 11 * * * * someScript2.sh 30 11 */2 * * someScript3.sh <-- ...
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Check if script is started by cron, rather than invoked manually

Is there any variable that cron set when it's running a program ? If the script is running by cron, I'll skip some parts; otherwise invoke those parts. How can I know if the bash script is started by ...
8
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3answers
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How to add unique id to file name in cron job?

My cronjob looks like this: 5 3 * * * mysqldump -u root test > /srv/backup/mysql_daily.dump How can I make filename unique for every time when cronjob writes mysql_daily.dump?
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Cron running job every 15 seconds

Could you advise me what to write in crontab so that it runs some job (for testing I will use /usr/bin/chromium-browser) every 15 seconds?
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1answer
25k views

As root, how can I list the crontabs for all users?

I have a script being run automatically that I can't find in the crontab for the expected users, so I'd like to search all users' crontabs for it. Essentially I want to run a crontab -l for all ...
8
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1answer
3k views

How to autostart a background program by a non-root user?

As a non-root user, I want to run a background job when the system boots. It's sort of a service which doesn't require root privilege. Is there a way to do it? One way is to put sudo -u user command ...
7
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2answers
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Can I automate tar's multi-volume-feature?

Ok, so I've just had a read through this page after a way to improve my current backup solution on my Debian server. Tar seems to be offering a quite nice multi-volume feature, although when I try it ...
7
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1answer
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Where to find the Crontab logs in CentOS

First of all I'm using CentOS [root@a etc]# cat system-release CentOS release 6.5 (Final) [root@a cron.daily]# ps -ef | grep cron root 982 1 0 Jun14 ? 00:01:15 crond root ...
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3answers
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/etc/cron.daily/foo : Send email to a particular user instead of root?

I'm running CentOS 5.5. We have several cronjobs stored in /etc/cron.daily/ . We would like the email for some of these cronjobs to go to a particular email address, while the rest of the emails in ...
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3answers
43k views

How to start a cron job without reboot?

I use a cron job to call offlineimap every 2 minutes: */2 * * * * /usr/bin/offlineimap > ~/Maildir/offlineimap.log 2>&1 I needed to kill the cron job to fix a problem. How can I then ...
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2answers
13k views

Can I change the default mail recipient on cron jobs?

I believe that if there is any output from a cronjob it is mailed to the user who the job belongs to. I think you can also add something like MAILTO=vivek@nixcraft.in at the top of the cron file to ...
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2answers
3k views

Have cron email output to MAILTO based on exit status

I have a cron job running a php command like this: php /path/to/script.php > dev/null This should send only STDERR output to the MAILTO address. From what I gather the php script is not ...
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1answer
3k views

List of modified files of the past 24 hours

Is there a reliable way to have a system that mails me the list of files that were modified in the past 24 hours inside a set of directories? (like /home/*/public_html/* and /home/*/*domains/*)
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Running a script during booting/startup; init.d vs cron @reboot

I am currently trying to understand the difference between init.d and cron @reboot for running a script at startup/booting of the system. The use of @reboot (this method was mentioned in this forum ...
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3answers
2k views

Where to put system cronjobs?

If I need a cronjob that runs at system level (i.e. not specific for a certain user) how do you suggest me to create it? running crontab -e as root appending it to /etc/crontab creating a file ...
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3answers
5k views

Crontab entry with hour range going over midnight

Is this valid crontab time specification, doing what is expected: 0 22-4 * * * Or is it necessary to do something like 0 22,23,0,1,2,3,4 * * *
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3answers
607 views

Create cron jobs to repeat every X units of time starting on an arbitary unit

I have a cron job on CentOS that I want to execute every 3 minutes but I have many other cronjobs that run at every 3 minutes starting from 0, 3, 6, 9... So, to avoid my server getting too ...
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2answers
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Location of the crontab file

as many (most?) others, I edit my crontab via crontab -e, where I keep all routine operations such as incremental backup, ntpdate, various rsync operations, as well as making my desktop background ...
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4answers
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Is setting a higher nice level for a process an effective way to reduce its impact on system load/CPU time?

I have an rsync cron job which is pushing the server load and triggering monitor alerts. If I set the job to be run with a high nice level, would that effectively reduce the impact it has on system ...
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3answers
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What's wrong with these two cron job's?

I have the following cron jobs defined. 55 8 * * 3 /usr/bin/php /home/mark/dev/processes/customClient/events.php > /home/mark/dev/processes/customClient/events-`date +%Y-%m-%d ...
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4answers
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How do I add an entry to my crontab?

I am using crontab for the first time. Want to write a few very simple test cron tasks, and run them. $crontab * * * * * echo "Hi" doesn't produce anything. crontab */1 * * * * echo "hi" says ...
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1answer
7k views

Meaning of “* */1 * * *” cron entry?

Somehow, I am finding it difficult to understand tweaking around * parameters with cron. I wanted a job to run every hour and I used the below setting: * */1 * * * But it does not seem to do the ...
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2answers
3k views

Open emacs in a terminal when editing crontab

I have setup emacs as my default editor in /etc/profile. When I want to use emacs in a terminal. I open it with the -nw option. How can I have the same behavior when doing a crontab -e preventing it ...
6
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3answers
3k views

Cron to not run on specific day but all other days

I have a cron setup to execute a bash script daily at 10pm. I have another cron setup to run monthly on the 1st of the month. Both crons launch a bash script, and the only different in the bash script ...
6
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2answers
12k views

How to find a cron job if you know the specific time it runs?

I've been using kSar to look at my servers resource use. There is a definite spike in process creation at 4:04AM daily. Cron seems to define the interval they should be run, but not the specific time ...
6
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2answers
1k views

script to check if SSL certificate is valid

I have several SSL certificates, and I would like to be notified, when a certificate has expired. My idea is to create a cronjob, which executes a simple command every day. I know that the openssl ...
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2answers
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System Crontab or Root Crontab

System crontab: /etc/crontab Root crontab: sudo crontab -u root -e Which way is preferred? As they all run tasks within administration privilege.
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How to get which version of cron daemon is running

Background: I am working on CentOS Details # cat /proc/version Linux version 2.6.18-308.4.1.el5PAE (mockbuild@builder10.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-52)) #1 SMP Tue Apr 17 ...
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2answers
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Logging ALL stderr output of crontab to file

For example, I can log stderr of one script in this way: * * * * * run_script.sh > /var/log.txt 2>&1 But I want to log stderr of all scripts in my crontab. I can append > /var/log.txt ...
6
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4answers
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Change the time zone of a cronjob

I have a cronjob which is executes every day at 9:00 AM of UTC-Time. I'm in GMT+1 so it executes at 10:00 AM local time. When there is the timezone change (to daylight saving time, DST), the cronjob ...
6
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1answer
23k views

How to run a cron job to execute every minute?

I am trying to create a directory having timestamp in its in name in the /home directory. I have created the following cron job as root user. But it's not running. What am I doing wrong? Following is ...
6
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2answers
603 views

systemd - Timer units that mimic anacron behaviour

I need to write a timer unit for a machine which is turned of frequently (e.g. classical desktop setup). This timer unit needs to be activated regularly but not very often (e.g. weekly, monthly). I ...
6
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1answer
10k views

mail: cannot send message: process exited with a non-zero status

I've had a cronjob working for about a fortnight without any problems. Then last night I checked I didn't get the email that I usually get. I went to the terminal to try send myself an email, I got ...
6
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2answers
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cronjob for automatic DB backup to date prefixed file

I am using the latest Linux Mint. I was wondering if it's possible to create a special cronjob for a database backup. In my /etc/cronjob file I have the following code: # Minute Hour Day of ...
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5answers
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How can I use cron to display messages on the screen via notify-send

I am toying around with notify-send and cron (on an Arch machine) and I can't figure out a way to combine them: I tried the solution given here and here, but neither worked. How can I use them? ...
6
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3answers
4k views

What could cause a cron to run twice at the same moment?

I have a cron that is setup to run every Monday at 1 AM 0 1 * * 1 /script/dir/script >> /script/dir/file.log After two years of running as expected, it ran twice on June 18, with the second ...
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1answer
133 views

How can I make `sudo crontab -e` use my `sudoedit` environment?

I've started using sudoedit <file> instead of sudo vim <file>. One of the advantages is that it uses my local ~/.vimrc. However, when using sudo crontab -e, it uses /root/.vimrc instead. ...
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4answers
1k views

A gzip process regularly runs on my system, how do I figure out what is triggering it?

For a while now, I have had the problem that a gzip process randomly starts on my Kubuntu system, uses up quite a bit of resources and causes my notebook fan to go crazy. The process shows up as gzip ...
5
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5answers
65k views

crontab -e , then 0 * * * * = every hour… Where is stored

After sudo crontab -e (it wrote "/tmp/crontab.XXXX70pN9h" 1L, 19C 1,1 All Then I saved the file. And to check..? (how? i don't know) And to check I ps -e | grep cron 29818 ? ...
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2answers
298 views

Upgrading packages automatically

I'm fairly new to using servers (debian 7) and I'm currently running cron-apt to e-mail me when there are new upgrades available. Is the following command safe to run when new upgrades are shown? ...
5
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2answers
402 views

cron every X exact meaning

In cron you can specify */n where n means every n times period, for instance in the first column is minute. */5 means every 5 minutes, but which minutes? 0, 5, 10, ...? What happens if the number ...
5
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3answers
17k views

executing a sh script from the cron

I have a test.sh script #!/bin/sh php /home/v/file.php sh /root/x/some.sh when I execute the file as root from command line it works. sh /home/v/test.sh when I set it to crontab -e (is the root ...
5
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3answers
6k views

How can I ensure my cronjob will run at specified time?

I'd like to know how I can check to see if my cronjob will run at the specified time I set it at. Is there anyway I can test this without having to wait for that time? Here are my crontab -l results: ...
5
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2answers
2k views

Execution order with multiple commands

I'm relatively new to Linux and I'm working on a CronTab for scheduled backups. I figured out how to do multiple sequential jobs with ; and &&, but I'm unsure how the dependency affects the ...
5
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2answers
3k views

How do the internals of the cron daemon work?

I want to know how cron works internally. Does the process keep checking the current time in an infinite while loop (thus continually consuming CPU cycles)? Or does some function generate an interrupt ...
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2answers
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why doesn't 0 0 * * 1 root hostname >> /tmp/hostname.txt work as a crontab?

0 0 * * 1 root hostname >> /tmp/hostname.txt The above cron entry should run midnight on monday and create a file in /tmp called hostname.txt with the output of the hostname command. But it is ...