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Questions tagged [cron]

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

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202
votes
3answers
492k 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?
172
votes
7answers
180k 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 ...
171
votes
9answers
375k 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?
135
votes
5answers
278k 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?
133
votes
6answers
356k 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 ...
117
votes
6answers
94k 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 ...
114
votes
11answers
224k 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 ...
113
votes
4answers
98k views

Day of week {0-7} in crontab has 8 options, but we have only 7 days in a week

Day-of-week: Allowed range 0 – 7. Sunday is either 0 or 7. I found this after Googling, my question is why should both values (0,7) correspond to Sunday?
105
votes
2answers
218k 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. ...
83
votes
2answers
31k 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 ...
81
votes
4answers
137k 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 ...
72
votes
4answers
183k 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 ...
70
votes
1answer
58k 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.
66
votes
13answers
57k 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. ...
64
votes
3answers
51k views

Recover cron jobs accidently removed with crontab -r

I entered crontab -r instead of crontab -e and all my cron jobs have been removed. What is the best way (or is there one) to recover those jobs?
64
votes
7answers
323k 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 ...
56
votes
2answers
9k views

Suspicious crontab entry running 'xribfa4' every 15 minutes

I wanted to add something to my root crontab file on my Raspberry Pi, and found an entry that seems suspicious to me, searching for parts of it on Google turned up nothing. Crontab entry: */15 * * * ...
51
votes
2answers
115k views

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 ...
48
votes
8answers
51k 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 ...
48
votes
3answers
122k 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 ...
46
votes
3answers
126k 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 users....
45
votes
4answers
51k 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 ...
41
votes
3answers
129k 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?
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 ...
37
votes
5answers
84k 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 ...
36
votes
1answer
142k views

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 ...
35
votes
1answer
41k views

How do I enable locate and queue the database to be built?

On a new Ubuntu 10.4 instance, I tried to use the locate command only to receive the error locate: can not stat () `/var/lib/mlocate/mlocate.db': No such file or directory from using this command on ...
35
votes
1answer
2k views

Why aren't crontabs stored in user home directories?

I'm curious to know: why are crontabs stored in /var rather than in the user's home directories? It makes it a total pain to isolate these files for upgrades but I suspect that there is a logical ...
34
votes
2answers
10k 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 ...
31
votes
12answers
20k 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 ...
31
votes
1answer
22k views

What's the meaning of the slash in crontab?

I have seen a crontab record in system. 0-55/5 * * * * root <command> I read the crontab -e example files and I know the first position stands for minute. But I cannot figure out the ...
30
votes
10answers
87k views

How to restart the Python script automatically if it is killed or dies

I am running my Python script in the background in my Ubuntu machine (12.04) like this - nohup python testing.py > test.out & Now, it might be possible that at some stage my above Python ...
30
votes
6answers
48k views

Crontab never running while in /etc/cron.d

Here's what I did on Debian Jessie: install cron via apt-get install cron put a backup_crontab file in /etc/cron.d/ However the task is never running. Here are some outputs: /# crontab -l no ...
29
votes
8answers
93k views

Why did my crontab not trigger?

I used crontab -e to add the following line to my crontab: * * * * * echo hi >> /home/myusername/test Yet, I don't see that the test file is written to. Is this a permission problem, or is ...
29
votes
1answer
38k 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 ...
28
votes
2answers
87k views

Is a restart of cron or crond necessary after each new schedule addition or modification?

When I schedule a job, some seem to be applied immediately, while others after a reboot. So is it recommended to restart cron (crond) after adding a new cron job? How to do that properly (esp. in a ...
27
votes
2answers
58k views

Cron log on debian systems

On Redhat systems cron logs into /var/log/cron file. What is the equivalent of that file on Debian systems?
22
votes
8answers
23k 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 ...
22
votes
3answers
21k views

Are multiple @daily crontab entries processed in order, serially?

I want two jobs to run sometime every day, serially, in exactly the order I specify. Will this crontab reliably do what I want? @daily job1 @daily job2 I'm assuming they run one after the other, but ...
21
votes
5answers
160k views

How do I create a service for a shell script so I can start and stop it like a daemon?

I'm using CentOS 7 what my aim is to create a cron for every five seconds but as I researched we can use cron only for a minute so what I am doing now is I have created a shell file. hit.sh while ...
21
votes
2answers
2k views

Can grep | crontab destroy all jobs?

My colleague ran grep | crontab. After that all jobs disappeared. Looks like he was trying to run crontab -l. So what happened after running the command grep | crontab? Can anyone explain?
21
votes
2answers
107k 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
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). ...
19
votes
3answers
26k 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/ ...
19
votes
2answers
6k views

Origin of the word cron?

Trying to settle a friendly argument. Is "cron" an acronym for something? Additionally, did it's current canonical name "cron" originate from something shortened for something like chronos or ...
18
votes
4answers
87k 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?
18
votes
1answer
5k views

Does systemd timer unit skip the next run if the process hasn't finished yet?

I want to use systemd to run a command every 5 minutes. However, there is a risk that occasionally the task may take longer than 5 minutes to run. At that point, will systemd start a second instance ...
18
votes
2answers
4k views

Suppress output unless non-zero exit code

What's the best way to suppress output (stdout and stderr) unless the program exits with a non-zero code? I'm thinking: quiet_success() { file=$(mktemp) if ! "$@" > "$file" 2>&1; then ...
18
votes
3answers
21k 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 * * *
18
votes
4answers
59k 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 ...