I used crontab to run a bash script once a day (at midnight). This worked successfully, but I didn't really think it through enough to realise that the script would not run if my computer happened to be off at midnight (or even asleep).
So I think that I have to keep the crontab entry (in case my computer is on) but I also want to make the bash script execute on startup (in case my computer was off) so that I have covered all my bases.
I saw online that to have my script execute on startup I should edit my /etc/rc.local file. My file now contains:
#! /bin/bash
bash /home/me/code.sh
exit 0
and my permissions are -rwxr-xr-x.
However, the script does not execute on startup. Is there something I'm doing wrong?
I guess you created the /etc/rc.local yourself right? AFAIK there isn't any in Ubuntu 18.04 anymore (as it is depricated). That's probably why it's not executed.
#reboot in crontab might be a possible solution for your problem.
Anacron is the answer for your problem. This is cron like system created exactly for tasks on machines not always on.
https://linux.die.net/man/5/anacrontab
I would like to use cron on my Mac. I choose it over launchd, because I want to be able to use my new knowledge on Linux as well. However, I cannot seem to get the crontab -e command to work. It fires up vim, I enter my test job:
0-59 * * * * mollerhoj3 echo "Hello World"
But after saving and quitting (:wq),
crontab -l
says:
No crontab for mollerhoj3
What am I doing wrong?
Just follow these steps:
In Terminal: crontab -e.
Press i to go into vim's insert mode.
Type your cron job, for example:
30 * * * * /usr/bin/curl --silent --compressed http://example.com/crawlink.php
Press Esc to exit vim's insert mode.
Type ZZ to exit vim (must be capital letters).
You should see the following message: crontab: installing new crontab. You can verify the crontab file by using crontab -l.
Note however that this might not work depending on the content of your ~/.vimrc file.
I've never had this problem, but I create a ~/.crontab file and edit that (which allows me to back it up, Time Machine or otherwise), then run
crontab ~/.crontab
Has worked for me for 20+ years across many flavors of unix.
NOTE: the answer that says to use the ZZ command doesn't work for me on my Mavericks system, but this is probably due to something in my vim configuration because if I start with a pristine .vimrc, the accepted answer works. My answer might work for you if the other solution doesn't.
On MacOS X, according to the crontab manpage, the crontab temporary file that gets created with crontab -e needs to be edited in-place. Vim doesn't edit in-place by default (but it might do some special case to support crontab -e), so if your $EDITOR environment variable is set to vi (the default) or vim, editing the crontab will always fail.
To get Vim to edit the file in-place, you need to do:
:setlocal nowritebackup
That should enable you to update the crontab when you do crontab -e with the :wq or ZZ commands.
You can add an autocommand in your .vimrc to make this automatically work when editing crontabs:
autocmd FileType crontab setlocal nowritebackup
Another way is to add the setlocal nowritebackup to ~/.vim/after/ftplugin/crontab.vim, which will be loaded by Vim automatically when you're editing a crontab file if you have the Filetype plugin enabled. You can also check for the OS if you're using your vim files across multiple platforms:
""In ~/.vim/after/ftplugin/crontab.vim
if has("mac")
setlocal nowritebackup
endif
The use of cron on OS X is discouraged. launchd is used instead. Try man launchctl to get started. You have to create special XML files that define your jobs and put them in a special place with certain permissions.
You'll usually just need to figure out launchctl load
https://www.unix.com/man-page/osx/1/launchctl/
http://nb.nathanamy.org/2012/07/schedule-jobs-using-launchd/
Edit
If you really do want to use cron on OS X, check out this answer: https://superuser.com/a/243944/2449
Difference between cron and launchd
As has been mentioned cron is deprecated (but supported), and launchd is recommended for OS X.
This is taken from developer.apple.com
Effects of Sleeping and Powering Off
If the system is turned off or asleep, cron jobs do not execute; they will not run until the next designated time occurs.
If you schedule a launchd job by setting the StartCalendarInterval key and the computer is asleep when the job should have run, your job will run when the computer wakes up. However, if the machine is off when the job should have run, the job does not execute until the next designated time occurs.
All other launchd jobs are skipped when the computer is turned off or asleep; they will not run until the next designated time occurs.
Consequently, if the computer is always off at the job’s scheduled time, both cron jobs and launchd jobs never run. For example, if you always turn your computer off at night, a job scheduled to run at 1 A.M. will never be run.
I did 2 things to solve this problem.
I touched the crontab file, described in this link
coderwall.com/p/ry9jwg (Thanks #Andy).
Used Emacs instead of my default vim: EDITOR=emacs crontab -e (I have no idea why vim does not work)
crontab -lnow prints the cronjobs. Now I only need to figure out why the cronjobs are still not running ;-)
In user crontab (crontab -e) do not put the user field.
Correct cron is:
0-59 * * * * echo "Hello World"
Syntax with user field is for /etc/crontab only:
0-59 * * * * mollerhoj3 echo "Hello World"
The error crontab: temp file must be edited in place is because of the way vim treats backup files.
To use vim with cron, add the following lines in your .bash_profile
export EDITOR=vim
alias crontab="VIM_CRONTAB=true crontab"
Source the file:
source .bash_profile
And then in your .vimrc add:
if $VIM_CRONTAB == "true"
set nobackup
set nowritebackup
endif
This will disable backups when using vim with cron. And you will be able to use crontab -e to add/edit cronjobs.
On successfully saving your cronjob, you will see the message:
crontab: installing new crontab
Source:
http://drawohara.com/post/6344279/crontab-temp-file-must-be-edited-in-placeenter link description here
Other option is not to use crontab -e at all. Instead I used:
(crontab -l && echo "1 1 * * * /path/to/my/script.sh") | crontab -
Notice that whatever you print before | crontab - will replace the entire crontab file, so use crontab -l && echo "<your new schedule>" to get the previous content and the new schedule.
As the previous posts didn't work for me because of some permissions issues, I found that creating a separate crontab file and adding it to the user's crontab with the -u parameter while root worked for me.
sudo crontab -u {USERNAME} ~/{PATH_TO_CRONTAB_FILE}
The above has a mix of correct answers. What worked for me for having the exact same errors are:
1) edit your bash config file
$ cd ~ && vim .bashrc
2) in your bash config file, make sure default editor is vim rather than vi (which causes the problem)
export EDITOR=vim
3) edit your vim config file
$cd ~ && vim .vimrc
4) make sure set backupcopy is yes in your .vimrc
set backupcopy=yes
5) restart terminal
6) now try crontab edit
$ crontab -e
10 * * * * echo "hello world"
You should see that it creates the crontab file correctly. If you exit vim (either ZZ or :wq) and list crontab with following command; you should see the new cron job. Hope this helps.
$ crontab -l
Use another text editor
env EDITOR=nano crontab -e
or
env EDITOR=code crontab -e
DISCLAIMER: I am not a Mac user. However, I have used crontab a great deal on Linux and similar systems. I presume that crontab on Mac works similarly.
A number of answers and comments suggest using an editor other than vim. That's fine, but there's no good reason that vim shouldn't work.
The cron system maintains a crontab for each user. The location of that file is unimportant; only the crontab implementation needs to know about it. cron provides an interface that allows users to request updates to their own crontabs.
The crontab -e command performs the following steps:
Copy the user's crontab to a temporary file.
Invoke the editor ($VISUAL or $EDITOR) on that temporary file.
When the editor command terminates, copy the temporary file back to the user's crontab (after doing some sanity checks).
Reload the user's crontab.
The vim editor, when you use it to edit a file, usually creates a new file with the same name. This shouldn't matter. The crontab -e command creates a temporary file, waits for the user to edit it, and then re-reads the temporary file by name. It doesn't keep the temporary file open while the user is editing it. If the Mac crontab implementation does this, I would argue that it's buggy. I'll also note that the original poster did not mention the "crontab: temp file must be edited in place" message; that was mentioned in a comment.
The most plausible explanation I can think of is that the OP was using gvim or something similar. gvim is a GUI version of vim, and if you invoke it from a shell prompt you'll get a new prompt immediately; it launches a GUI editor that runs in the background. If you use crontab -e and it tries to use gvim to edit the temporary file, then crontab will see the editor command terminating immediately, and it won't see any updates.
In fact, I was able to reproduce the problem by invoking
VISUAL=gvim EDITOR=gvim crontab -e
on a Linux system. (Again, I'm not a Mac user, and there might be some Mac-specific weirdness that I'm missing.)
A number of other answers and comments suggest using a different editor. That shouldn't be necessary. Any correctly working text editor should work with crontab -e -- as long as the editor command doesn't terminate until after the temporary file is updated. I've always had vim (or vi or nvi) as my default editor, and I've never had a problem using it with crontab.
The crontab line in the question:
0-59 * * * * mollerhoj3 echo "Hello World"
appears to be intended for a system crontab The first 5 fields specify the schedule, and the 6th is the user name. A normal user crontab does not have this 6th field, since the crontab command keeps track of the owner (the account that ran the crontab command). 99% of the time, you don't need to worry about system crontabs. Even root can use the crontab command to install a user crontab for the root account. However, this alone doesn't explain the problem seen by the OP; the syntax is valid for a user crontab, but it will attempt to invoke a command called mollerhoj3 with arguments echo "Hello World". That will cause an error when the command is scheduled, not when the crontab is created or updated.
Finally, a bit of advice that doesn't address the original question. Using crontab -e can be slightly dangerous, since it's easy to damage or destroy your crontab without meaning to. Instead, I suggest keeping a file in your home directory (possibly maintained in a version control system) and applying the contents of that file using crontab filename. For example, you might create and edit $HOME/.crontab, and run crontab $HOME/.crontab after updating it.
The question is over 9 years old, but the original poster is still more or less active (but may not have the same system).
#Hanzaplastique answer in this comment worked for me: export EDITOR=nano
I'm trying to get a file to be automatically run by crontab, contents like so:
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
*/5 * * * * php /path/to/script
I've put this file called prod.cron into the /etc/cron.d folder but can't seem to get it to run on it's own. Running the script directly via command line shows that it works okay, but not sure if the files in cron.d get auto detected or do I need to do something else to init them?
Note that directory /etc/cron.d is intended to be used by packages, crontabs should be installed into an users crontab. That being said, check out the following Cron Issues:
The script is not having execute permissions. Use chmod a+x to provide permissions.
In the case of php, perl or other scripting language, the path to interpretor or program is not correct. Always provide actual path to
the interpretor while defining command to run in cron. To find out
where the program is located, use whereis command. For e.g.
for php, whereis php. for perl, whereis php, etc.
The environment variables required to run the script are unavailable. The cron doesn't use the same environment of a user. It
uses its own environment while running the commands. So the variables
defined in .login or .profile are not visible to him. The most common
issue is related to PATH variable which is not similar.
There are two flavors of cron file.
Files installed under /etc/cron.d are system cron files. They require the 6th field on each line to be the user account used to run the command. See other files under /etc/cron.d for examples.
Non-system cron files just have the usual 5 fields to specify when the job runs, followed by the command to run. They're installed by the crontab command, executed by the user account that will run the command(s). This is probably what you wnat to use.
Either add root as the 6th field of the relevant line, or run crontab prod.cron as root (or as whatever account should run the command).
And of course make sure the php command is in the specified $PATH.
I have crontab running a shell script periodically. I need the script to run in the same environment that I usually log in. Can I just simply add this line in 2nd line of the script (after shebang).
source /home/<my username>/.cshrc
Or what's the proper way to set the cron shell process to use my login environment?
PS: I am quite sure which exactly setting is needed by my script, so I can only source the whole .cshrc.
Try something like that:
sudo su - <user> -c <cmd>
Of course you have to alter the sudoers file first.
Take a look at the man page.
hth
I'm trying to write a web frontend for Crontab in Ruby using the excellent CronEdit gem. I went through Dillon Cron's crontab source code and found that it updates a particular file so that the daemon will refresh the cron list during the next sweep.
In man crontab for VixieCron, it says:
Additionally, cron checks each minute to see if its spool directory’s modtime
(or the modtime on /etc/crontab) has changed, and if it has, cron will then
examine the modtime on all crontabs and reload those which have changed.
Thus cron need not be restarted whenever a crontab file is modified. Note that
the crontab(1) command updates the modtime of the spool directory whenever it
changes a crontab.
Is there any platform (Ubuntu, Red Hat, ArchLinux, Mac OS X) independent way to ensure that after manually editing the Cron file, the daemon refreshes it without fail?
No, there isn't. If you know it's VixieCron, then update the timestamp of the directory. Otherwise, you might be able to fake it: Set the env variable EDITOR before you invoke crontab -e (which should bring up an editor for the crontab).
The idea is to set the editor to some program which makes the change. crontab -e will wait for the editor to terminate and reread the file and tell cron that something has changed.
If you have an old version of cron, though, you must still restart it. But I doubt that you can find such ancient versions on anything that runs Linux or Mac OS X.
Sane modern linux distros have /etc/cron.d/ directory where you can put your crontab entry as a separate file. If I recall correctly the new cronfile gets read within 2 minutes of being written
Thank you very much gnibbler and Aaron. I just went through the source code for both 'whenever' and 'cronedit' gems for Ruby. Both of them does a 'crontab -' which replaces the existing cron file with the updated cron entries. That means contrary to my original question, these libraries make use of the standard crontab tool which in turn would do whatever specifics necessary to refresh the daemon.
I think the best platform-independent, and cron (dillon, vixie, mcron etc.) agnostic way to refresh the daemon is to always use the associated crontab utility. Even when editing programmatically, the user-program must pass the new cron file to the crontab utility which would do whatever is required by that specific platform/cron.
#Mark, thank you for the comments. However, I'm trying to provide a simple web frontend that the user can customize through the www just like editing the crontab file directly.
Thank you so much for your responses!
If this is that important, why not use a different lever? In other words, there are two options:
crontab 1: /do/some/very/specific/thing with specific parameters that i need to change etc.
crontab 2: /do/what/needs/to/be/done
In #2, the job is responsible for determining at run time what needs to be done and doing it. With this design, the notion of needing to understand how crontab works on some detailed level is irrelevant.