By accident made 2 different crontabs:
First with sudo crontab -e
Second with crontab -e
Just asking what happens (because did not find an explanation):
1) If they are different, are both being executed?
2) If both are identical, which one is executed? Or prone to a 'collision'?
Running sudo crontab -e will create cron tasks for the root account, and these tasks will be executed as root. Running crontab -e without sudo will create cron tasks for your user, and the tasks will be executed as that user.
Each user can have his own crontab. The first one will be executed from root, as you ran it with sudo, and the second one from your own user.
Related
How can I delete or clear all the cron job that I made previously and just run new cron job that I assigned? I'm using crontab -r but it just clear in the crontab display, but it still runs that cron job and the previous cron job that I have already deleted by using that code.
After I clear cron job using crontab -r, I run crontab -l and it shows this output.
No crontab for trygcp
Use this command,
crontab -e
to access crontab, in there you can deleted specific line or job you created.
About the output you are getting, that only means there is no crontab created under the username trygcp
What you can do is this:
crontab -u [username] -e
Where:
-u define user
-e edit user's crontab
This command will create a crontab under your username, but remember you must have root privilege for you to do this.
I want to edit system cron tab (/etc/crontab). I read that crontab -e is the best way to edit crontab and you need not restart cron services if you edit this way. However I am not able to edit /etc/crontab using crontab -e (this command edits the crontab associated with the user, not system crontab). So is there any better way of editing /etc/crontab (other than using VI editor- which I am doing now). Do I need to restart cron services if I edit /etc/crontab using VI edior?
There are two ways of cronjobs, one is by editing /etc/crontab and sending a SIGHUP the cron daemon. The other way is to use crontab -e to edit
a crontab entry, which is done for the current user or the one mentioned with -u. The -u option can only be used by root. The crontabs
created this way can be found in the directory
/var/spool/cron/crontabs/
and are named after the user with which uid the jobs will be started. In this case you don't need to SIGHUP cron, a normal user can't do this anyway.
Note: The syntax is slightly different to /etc/crontab: You can't enter an other user name to execute the cronjob.
You could do something like this
echo "0 23 * * * yum -y update > /dev/null 2>&1" >> /var/spool/cron/root
Then verify with
crontab -l
I noticed that when I typed sudo crontab -e I dont see my cron command, but when I do only crontab -e there is my command.
Is there a difference between the 2? If there is, where should I put my cron command, should it be in sudo or without the sudo?
Thanks!
Is there a difference between the 2?
Yes, indeed they are different.
The difference is that with sudo crontab -e the commands are schedule with root user's credentials. So that the commands in the sudo's cron table are executed as root user.
But with crontab -e, the commands are scheduled with the regular user who is logged in.
Where should I put my cron command, should it be in sudo or without the sudo?
Well, the answer to this depends on the type of command you want to run.
If the command required sudo access then sudo crontab -e should be used.
Else if the cron command doesn't require any special permission then use crontab -e.
Example:
If the ethernet network interface eth0 should be disabled or enabled at specific time then you would use the command
ifconfig eth0 up or ifconfig eth0 down
As the above commands require special permission (sudo), these commands are supposed to added to sudo's cron tab
Any other command which require minimal permission or no permission like removing a file from tmp directory like $ rm /tmp/somefile use the regular user's crontab.
Main part of the problem is to take care of the user with whom you wanna make your things done. Otherwise it will not trigger your cron job. And do make sure that you write output of your command in any file. It will help you to debug the problem which most probably might relate to your relative paths.
That's what I faced difficulties in. You can move forward following the below step:
identify your username with which you wanna go. Use whoami command.
Turn to your selected user mode and type crontab -e.
And append line < cron-schedule your-command >> output_filename.cron 2>&1 >
That's it.
Thanks!
I developed a script in which I add lines to the crontab file with echo command and I remove lines with sed command.
I do not know the risk of that especially that I find in some web site that we have to edit crontab file with
crontab -e
What is the risk of does not using crontab -e?
Are there a risk that my edit will not taken account in the cron
schedule?
Should I restart cron with /etc/init.d/cron restart?
The main risk to not using crontab to edit or replace cronfiles is that directly writing to the cronfile (including using sed to do so) does not lock the file, and therefore two simultaneous edits could have unpredictable and even disastrous consequences.
You don't have to use crontab -e; the following forms of editing are semi-safe, in the sense that they won't randomly combine two edits. (But they are still unsafe; an edit could be overwritten):
To add lines:
{ crontab -u user -l; echo "$this"; echo "$this_too"; } | crontab -u user -
To delete lines or do more complicated edits:
crontab -u user -l | sed "$my_wonderful_sed_script" | crontab -u user -
In any case, you don't need to restart cron. It will notice the changed modification time of the cronfile.
When editing the crontab file using your regular editor, the schedule will not be updated. The system will still do the scheduled tasks as before the edit. This will drive the administrator mad.
When cron restarts, such as a reboot or a restart of the process, the current crontab files will be read and processes are scheduled as described in the current present files.
I remember sending a 'kill -HUP' or 'kill -15' to the PID of the cron process to force the process flushing the cache and reading the crontab files again.
I'm trying to make cron jobs or task schduler working, but I can not figure out why my script is not taken in consideration.
I'm trying to simply archive a folder with:
tar -cvf /volume1/NetBackup/Backups/Monday.tgz /volume1/NetBackup/Backups/ns3268116.ovh.net/
Each time the script starts working but cannot achieve the work. Either with task scheduler or crontab, a file Monday.tgz is created in folder /volume1/NetBackup/Backups/, but this file is only 1024 bytes.
Synology Cron is really fussy.
Here are my own personal notes for Synology DS413j, DSM 5.2:
Hand edit /etc/crontab as root, crontab -e isn't available
Ensure you use tabs not spaces to separate the columns
Your crontab changes may not survive a reboot if there are syntax problems
The who column in crontab may not be reliable. Use root in the who column and /bin/su -c '<command>' <username> to run as another other user
remember that it uses ash not bash so check for bashisms, e.g use >> /path/to/logfile 2>&1' not&>> /path/to/logfile`
It doesn't support 'MAILTO='
you need to restart crond synoservicectl --reload crond for the new crontab to take effect
You may try adding some diagnostics to it. For instance:
Add MAILTO into the crontab file (on top of crontab -e) to receive cron errors by email:
MAILTO=username#domain.com
Redirect output of your tar command to the file:
your command > ~/log.txt 2>&1
Check cron log and look for anomalies. For instance (it may depend on your configuration):
/var/log/cron.log
You may also try searching through /var/log/messages at the time of your cron job.
Is volume1 a resource on remote host? If yes, it is worth checking this part of the system.
I agree about the really nagging nature of Crontab on Synology Linux OSs.
I would certainly suggest to create de desired job as a .sh shell script and call it via CRON task inserted by using the GUI, as suggested here.
As for today (March 2017) is the best method I have found, since working with crontab via CLI is nearly a pain.