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.
Related
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.
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 am trying to run a shell script on crontab on Ubuntu platform. I have tried googling and other links but nothing has helped so far.
This is my crontab:
*/2 * * * * sudo bash /data/html/mysite/site_cleanup.sh
This is the content of my sh file:
#!/bin/sh
# How many days retention do we want ?
DAYS=0
# geting present day
now=$(date +"%m_%d_%Y")
# Where is the base directory
BASEDIR=/data/html/mysite
#where is the backup directory
BKPDIR=/data/html/backup
# Where is the log file
LOGFILE=$BKPDIR/log/mysite.log
# add to tar
tar -cvzf $now.tar.gz $BASEDIR
mv $now.tar.gz $BKPDIR
# REMOVE OLD FILES
echo `date` Purge Started >> $LOGFILE
find $BASEDIR -mtime +$DAYS | xargs rm
echo `date` Purge Completed >> $LOGFILE
The same script runs from a terminal and gives the desired result.
Generic troubleshooting for noninteractive shell scripts
Put set -x; exec 2>/path/to/logfile at the top of your script to log all subsequent commands to a file as they're run. If this doesn't work, you'll know that your script isn't being run at all; if it does, you'll know where it fails and how.
If this is a personal crontab
If you're running crontab -e as a user (without sudo), then the crontab being modified is one for commands run with that user's permissions. Check that file permissions allow that user to modify the content in question (which, if these files are in a cgi-bin directory, may require being run by the same user as the web server).
If your intent is to have commands run as root, rather than as your own user, be sure you use sudo when editing the crontab to edit the system crontab instead (but please take care as to your script's correctness in this case -- carelessness such as missing quotes or lack of appropriate precautions in xargs usage can cause a script to delete the wrong files if malicious filenames are created):
sudo crontab -e ## to edit the system (root) crontab
...or, if you're cleaning up files owned by the apache user (for example; check which account is correct for your own operating system and web server):
sudo -u apache crontab -e ## to edit the apache user's crontab
Troubleshooting for a system crontab
Do not attempt to put a sudo command within the commands run by cron; with sudo's default configuration, it requires a TTY (a keyboard and screen) to be attached to a session in order to run. Thus, your crontab line should not contain sudo, but instead should look like the following:
*/2 * * * * bash /data/html/mysite/site_cleanup.sh
Your issue is likely coming from the sudo call from your user level cron. Unless you've gone through and edited the bashrc profile to allow that script to run without sudo it'll hang up every time.
So you can lookup how to run a script with no password by modifying the bashrc profile, remove the sudo call if you aren't doing something in your script that calls for Super User permissions, or as a last ditch, extremely bad idea you can call your script from root's cron by doing sudo crontab -e or sudo env EDITOR=nano crontab -e if you prefer nano as your editor.
try to add this line to the crontab of user root and without the sudo.
like this:
*/2 * * * * bash /data/html/mysite/site_cleanup.sh
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.
I have following questions on cron.
What is the preferred way for automating cron jobs? Using a) crontab command-line options (eg. crontab -e) or b) editing /etc/crontab. What is the difference between the two? It's not exactly clear to me.
Is crontab user specific? If I am logged in as a a user say "anup", and add jobs using crontab -e, will the job be user-specific? However, in some of the cron examples I checked online, username is provided as a field between the time string and the command to be executed.
Can the 'Mail to user" option be controlled for each job? As in, for job 1: MailTO: root for job 2: MailTO: anup.
The crontab utility is a commandline tool that maintains the crontab files for individual users.
crontab -l lists/views the crontab for the current user
crontab -e edits the crontab
You can type man crontab for full documentation on most linux/mac systems.
The crontab is specific to the user. If you're logged in as anup, then crontab -e will edit anup's crontab file. You can specify the user with the -u flag (crontab -u)
I'm not 100% sure, but I believe that you can specify a new MAILTO= setting and it will take effect for all processes executed afterwards.