How to disable crontab “-r” option in Linux ?
In this article, we will look at a trick how to disable crontab “-r” option in Linux.
“E” and “R” lies nearby, hence there are chances while typing “crontab -e”, we run “crontab -r” and it will remove the crontab file.
To prevent this, we will add a function to /etc/profile file to enable this option system-wide.
Lets see the usage of crontab -l, -r, options.
General Crontab commannd Usage
Here we will see how crontab works.
### Lists crontab file [root@nglinux ~]# crontab -l 1 1 1 1 1 echo "hello" [root@nglinux ~]# ### removes crontab file [root@nglinux ~]# crontab -r [root@nglinux ~]# ### Now list again, it will say no crontab for root user. [root@nglinux ~]# crontab -l no crontab for root [root@nglinux ~]#
Different options of crontab file
-e (edit user's crontab) -l (list user's crontab) -r (delete user's crontab) -i (prompt before deleting user's crontab) -s (selinux context)
Creating custom crontab command
[root@nglinux ~]# cat /etc/profile | tail -10
function crontab()
{
if [ $1 == "-r" -o $1 == "-sr" -o $1 == "-rs" ]; then
echo "-r option removes the crontab file."
echo "To remove the file use the option '-ir' to interactively remove crontab file"
else
command crontab $1
fi
}
[root@nglinux ~]#
Output/Usage of Crontab function
### Usage via root user [root@nglinux ~]# crontab -l no crontab for root [root@nglinux ~]# crontab -r -r option removes the crontab file. To remove the file use the option '-ir' to interactively remove crontab file ### usage via nglinux user [root@nglinux ~]# su - nglinux Mysql password is root/redhat PHPMyAdmin can be accessed at http://localhost/phpmyadmin Apache and FTP Server already setup. Your IP addr:10.0.2.15 addr:172.21.49.107 NGEL System Console can be accessed at URL http://localhost/system Run NGELINUX_HARDDISK_INSTALL to create partitions and install this live CD on your system hard disk Run NGELINUX_INSTALL to copy block by block your ISO file to a USB or Complete Hard disk [nglinux@nglinux ~]$ crontab -l no crontab for nglinux [nglinux@nglinux ~]$ crontab -r -r option removes the crontab file. To remove the file use the option '-ir' to interactively remove crontab file [nglinux@nglinux ~]$