Sticky bit Permissions

What are sticky bit?

Files located in a directory with the sticky bit set can only be deleted or renames by the owner of the file or by the root user.

How to set Sticky bit?

chmod +t directory

How to Remove the Sticky bit Option

chmod -t directory

The sticky bit shows up in the execute position of the “other” as in Owner, Group, Other permission.

u=rwx,g=rwx,o=rwt

Crontab Visual Format

* * * * * *
| | | | | | 
| | | | | +-- Year              (range: 1900-3000)
| | | | +---- Day of the Week   (range: 1-7, 1 standing for Monday)
| | | +------ Month of the Year (range: 1-12)
| | +-------- Day of the Month  (range: 1-31)
| +---------- Hour              (range: 0-23)
+------------ Minute            (range: 0-59)

Clean up Your Boot Partition Ubuntu

If you constantly run out of space in the boot partition, you might need to run the following command to cleanup the boot partition.

First, list all installed kernels

dpkg -l linux-image-* | grep ii

Second, delete the chosen old kernel 

apt-get purge linux-image-4.4.0-XXXX*

Other command worth noting:

apt-get autoremove

or 

apt-get --purge autoremove

Cleanup this file below by removing old kernel entries.
/etc/apt/apt.conf.d/01autoremove-kernels

or

Remove the old kernels files manually
You can also remove the old kernels manually. I suggest leaving the older one and the latest.
Delete the kernels in between.