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Questions tagged [cron]

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

76
votes
4answers
134k views

Open a window on a remote X display (why “Cannot open display”)?

Once upon a time, DISPLAY=:0.0 totem /path/to/movie.avi after ssh 'ing into my desktop from my laptop would cause totem to play movie.avi on my desktop. Now it gives the error: No protocol ...
105
votes
6answers
82k views

How can I execute `date` inside of a cron tab job?

I want to create a log file for a cron script that has the current hour in the log file name. This is the command I tried to use: 0 * * * * echo hello >> ~/cron-logs/hourly/test`date "+%d"`.log ...
30
votes
12answers
18k views

Using notify-send with cron

I am using Arch Linux with KDE/Awesome WM. I am trying to get notify-send to work with cron. I have tried setting DISPLAY/XAUTHORITY variables, and running notify-send with "sudo -u", all without ...
64
votes
13answers
56k views

Correct locking in shell scripts?

Sometimes you have to make sure that only one instance of a shell script is running at the same time. For example a cron job which is executed via crond that does not provide locking on its own (e.g. ...
12
votes
3answers
14k views

What's wrong with these two cron jobs?

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 --date='...
4
votes
3answers
13k views

Run a GUI program at startup

I am using Ubuntu 14.04. I wrote a small script named trial. The contents of the script are as follows: #!/bin/sh SHELL=/bin/sh PATH=/bin:/sbin:/usr/bin:/usr/sbin sh -c firefox I copied the ...
16
votes
4answers
81k views

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?
12
votes
2answers
14k views

Bash Script on Startup? (Linux)

Is there any way to make/run a bash script on reboot (like in Debian/Ubuntu for instance, since thats what my 2 boxes at home have) Also, any recommended guides for doing cron jobs? I'm completely ...
61
votes
7answers
302k views

crontab's @reboot only works for root?

man 5 crontab is pretty clear on how to use crontab to run a script on boot: These special time specification "nicknames" are supported, which replace the 5 initial time and date fields, and ...
98
votes
11answers
207k views

How can I run a cron command with existing environmental variables?

How can I run a cron command with existing environmental variables? If I am at a shell prompt I can type echo $ORACLE_HOME and get a path. This is one of my environmental variables that gets set in ...
94
votes
2answers
200k views

How to redirect output to a file from within cron?

I have a backup script which I need to run at a particular time of a day so I am using cron for this task and from within cron am also trying to redirect the output of backup script to a logfile. ...
36
votes
3answers
118k views

Crontab job start +1 min after @reboot

Need a script executed at each reboot in +1 minute. I placed a record @reboot but it is too early for my script. How to execute it sometime after reboot?
43
votes
6answers
47k views

cron ignores variables defined in “.bashrc” and “.bash_profile”

I have defined "SHELL" variable in /etc/crontab file: [martin@martin ~]$ grep SHELL /etc/crontab SHELL=/usr/local/bin/bash [martin@martin ~]$ file /usr/local/bin/bash /usr/local/bin/bash: ELF 32-bit ...
10
votes
2answers
3k views

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 ...
34
votes
2answers
8k views

Where is cron's PATH set?

Cron doesn't use the path of the user whose crontab it is and, instead, has its own. It can easily be changed by adding PATH=/foo/bar at the beginning of the crontab, and the classic workaround is to ...
9
votes
2answers
24k views

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.
12
votes
3answers
57k 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 ...
3
votes
2answers
11k views

Run gui application on startup

I can run a script at boot by adding the following line to my crontab: @reboot perl /path/script That works fine. But the problem arises when I try to run a gui application such as gmail notify. It ...
0
votes
1answer
771 views

What is causing my “Unexpected EOF Error while looking for …” error? [duplicate]

I am getting an issue while running a cron job for exporting all databases on my Godaddy Shared hosting Cpanel account. But I have trouble finding the syntax error in below command. Same command is ...
-1
votes
2answers
283 views

how to properly log the output of a console program that frequently updates “parts” of the screen, resulting in a messy log file?

I have some Java executable (jar) that is run my some shell script from a cron job once every night. That executable does not print log statements "as usual" just by printing them out in a sequential ...
129
votes
6answers
328k views

What does '>/dev/null 2>&1' mean in this article of crontab basics? [duplicate]

I am reading an article about crontab There is something about disabling automatically sending emails. Disable Email By default cron jobs sends an email to the user account executing the ...
152
votes
7answers
166k views

What is the 'working directory' when cron executes a job?

I have a script that works when I run it from the command line, but when I schedule it with cron I get errors that it cannot find files or commands. My question is twofold: When I schedule a cron ...
162
votes
9answers
353k views

Where are cron errors logged?

If I setup cron jobs incorrectly they appear to silently fail. Where should I look for an error log to understand what went wrong?
34
votes
5answers
82k views

Using the system date / time in a Cron Script

I'm setting up a Cronjob that will backup a MySQL database I have in my server, but I don't want it to keep overwriting the same file over and over again. Instead, I want to have an array of backups ...
28
votes
1answer
36k views

Why does cron silently fail to run sudo stuff in my script?

I have a script run from a non-privileged users' crontab that invokes some commands using sudo. Except it doesn't. The script runs fine but the sudo'ed commands silently fail. The script runs ...
19
votes
4answers
2k views

Path independent shebangs

I have a script that I want to be able to run in two machines. These two machines get copies of the script from the same git repository. The script needs to run with the right interpreter (e.g. zsh). ...
12
votes
3answers
30k views

how to set crontab PATH variable

I had a problem running a script from crontab. After some research I understood the problem was because PATH parameter doesn't include /sbin. I looked what it does include in /etc/crontab: PATH=/...
4
votes
2answers
7k views

Why can't cron job find basic Linux commands? [closed]

I'm trying to set up a cron job to run a PHP script daily as part of a web-based booking system. It's been running perfectly for several years on a different Apache server using this in the crontab: ...
2
votes
1answer
2k views

Keeping track of service status continuously

I need to monitor the status of nagios service (Because, whenever I make any changes in configuration and apply the new configuration, I would find nagios service stopped). If found in 'stopped' state,...
184
votes
3answers
466k views

How can get a list of all scheduled cron jobs on my machine?

My sysadmin has set up a bunch of cron jobs on my machine. I'd like to know exactly what is scheduled for what time. How can I get that list?
68
votes
4answers
174k views

How do I completely silence a cronjob to /dev/null/?

On my Ubuntu-Desktop and on my debian-server I have a script which needs to be executed each minute (a script that calls the minute-tic of my space online browsergame). The problem is that on ...
38
votes
15answers
10k views

Run unix command precisely at very short intervals WITHOUT accumulating time lag over time

Question I'd like to be able to run a UNIX command precisely every second over a long time period. I need a solution, which does not lag behind after a certain time, because of the time the command ...
66
votes
1answer
54k views

How to change cron shell (sh to bash)?

Is it possible to make commands in crontab run with bash instead of sh? I know you can pass commands to bash with -c, but that's annoying and I never use sh anyway.
41
votes
4answers
47k views

How can I tell cron to run a command every other day (odd/even)

When configuring cron to run a command every other day using the "Day of Month" field, like so: 1 22 */2 * * COMMAND it runs every time the day of month is odd: 1,3,5,7,9 and so on. How can I ...
12
votes
6answers
6k views

CronJob every 25 minutes

I want to know whether there is any easier way to run a job every 25 minutes. In cronjob, if you specify the minute parameter as */25, it'll run only on 25th and 50th minute of every hour
14
votes
1answer
11k 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 ...
3
votes
4answers
10k views

How to display a (zenity/GUI) dialog to the user after a root cron task has completed

I have a simple periodic cron task that must run as root. I want to use Zenity (or similar) to display a GUI informational dialog to user 1000 (or logged in user or all users) when the cron task ...
11
votes
5answers
9k views

command not running in cron (systemctl suspend)

I have this cronjob set : * * * * * /usr/bin/systemctl suspend And it is not working. But I can run it in a shell and it works. I don't understand what could be not working. EDIT Redirecting error ...
14
votes
2answers
51k views

What are the runtime permissions of a cron job?

When a cron job runs with what privilege does it execute? I'm not sure about that. Is it with the same privileges of the user that added it via crontab -e?
6
votes
2answers
4k views

How to access X display from a cron job when using gdm3? [duplicate]

Possible Duplicate: Open a window on a remote X display (why “Cannot open display”)? I'm trying to run a cron job that needs access to my X session. I know my X session will always be ...
5
votes
1answer
7k views

How are files under /etc/cron.d used?

How are files under /etc/cron.d used? From https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/ cron reads the files in /etc/cron.d/ directory. Usually system daemon ...
4
votes
1answer
15k views

Why isn't this crontab job running

I have a cron job that runs every minute on an Ubuntu 12.04 box $sudo crontab -e * * * * * mylogin /pathto/file.sh > /log/filelog If I run file.sh, the bash script does some stuff and echos out ...
2
votes
3answers
1k views

Cron only occasionally sends e-mail on output and errors

On Debian 8.1, I'm using a Bash feature to detect whether the stackoverflow.com website is reachable: (echo >/dev/tcp/stackoverflow.com/80) &>/dev/null || echo "stackoverflow unreachable" This is ...
75
votes
2answers
27k views

Cron vs systemd timers

It was recently pointed out to me that an alternative to cron exists, namely systemd timers. However, I know nothing about systemd or systemd timers. I have only used cron. There is a little ...
47
votes
3answers
117k views

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 ...
110
votes
3answers
239k views

how can I make cron run a job right now, for testing/debugging? without changing the schedule!

I have a cron job that is scheduled to run everyday, other than changing the schedule, is there any other way to do a test run of the command right now to see if it works as intended?
22
votes
8answers
22k views

Check if script is started by cron, rather than invoked manually

Is there any variable that cron sets when it runs a program ? If the script is run by cron, I would like to skip some parts; otherwise invoke those parts. How can I know if the Bash script is started ...
21
votes
2answers
105k views

Cron job to delete files older than 3 days

I need to remove files older than 3 days with a cron job in 3 different directories. (these 3 directories are children of a parent directory /a/b/c/1 & /a/b/c/2 & /a/b/c/3) Can this be done ...
19
votes
3answers
25k views

Does RHEL/CentOS execute all cronjob files under /etc/cron.d/*, or just some of them?

This is a Red Hat Enterprise Linux 5 system (RHEL). We manage this system using CFengine. We have several cronjobs which are running twice as often as usual. I checked the cronjobs under /etc/cron.d/ ...
16
votes
8answers
14k views

cron Vs. sleep - which is the better one in terms of efficient cpu/memory utilization?

The Case: I need to run some commands/script at certain intervals of time and for this I have two options: set up a cron-job implement a loop with sleep in the script itself. Question: Which is ...