Where it is the crontab file in Ubuntu?

/var/spool/cron/crontabs/{user account}

Example

Where it is the crontab file of the luizcgjr account?

/var/spool/cron/crontabs/luizcgjr

Source: http://www.cyberciti.biz/faq/where-is-the-crontab-file/

How to print the first and last parts of a file in Linux

First part

1. Open terminal
2. Type
   
   
   head -n {n} {file}

{n} is the number of lines to return

{file} name of the file

Last part

1. Open terminal
2. Type
   
   
   tail -n {n} {file}

{n} is the number of lines to return

{file} name of the file

Example

Print the first 10 lines of the blogger.log file

head -n 10 blogger.log

Print the last 10 lines of the blogger.log file

tail -n 10 blogger.log

Source: http://linux.die.net/man/1/head
http://linux.die.net/man/1/tail

How to fix e-mail client error: Your IMAP server wants to alert you to the following: Please log in via your web browser: https://support.google.com/mail/accounts/answer/78754 (Failure)

1. Go to https://www.google.com/settings/security/lesssecureapps
2. In Access for less secure apps, check Turn on 
3. Go to https://accounts.google.com/b/0/DisplayUnlockCaptcha
4. Click Continue

Source: https://productforums.google.com/forum/#!topic/gmail/oiQxxrovkHs

How to reinstall a package in Ubuntu

1. Open terminal
2. Type
   
   
   sudo apt-get install --reinstall {package}

{package} is the package name that you want to reinstall

Example

I want to reinstall firefox

sudo apt-get install --reinstall firefox

Source: http://askubuntu.com/questions/89638/how-to-completely-uninstall-and-reinstall-firefox