Set time zone on Raspberry pi

Run this command which should work in most of distro.
Select the correct Zone that you wish to apply:

Example (London):

cp /usr/share/zoneinfo/Europe/London /etc/localtime

How to re-enable the systray (indicator panel) on Ubuntu 14.04

Installation in the terminal:

sudo apt-add-repository ppa:fixnix/indicator-systemtray-unity
sudo apt-get update
sudo apt-get install indicator-systemtray-unity

Once installed, you can enable it by this command:

gsettings list-recursively net.launchpad.indicator.systemtray

If you wish to remove it, run this command:

sudo apt-get --purge remove indicator-systemtray-unity

Sendmail is only accepting connections from localhost

By default configured to accept connection from local system (127.0.0.1). This should avoid open mail relay problem.

To allow connections from ALL hosts/LAN IPs open sendmail.mc file (login as the root):

# vi /etc/mail/sendmail.mc

Look for line that read as follows:

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

Comment or remove above line and insert new line that read as follows:

DAEMON_OPTIONS(`Port=smtp,Name=MTA')dnl

Above line will force to accept connection from any host. Save the file. Regenerate sendmail configuration file using m4:

# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

If this command is resulting by giving such of error as below, this means that the file

/etc/mail/sendmail.mc:10: m4: cannot open `/usr/share/sendmail-cf/m4/cf.m4': No such file or directory

Then, this means that the sendmail.cf.xx rpm package is missing and require to be installed.

In my case, I had to mount the cdrom, and look for this rpm file:

sendmail-cf-8.13.8-2.el5.i386.rpm

Restart sendmail service :

# /etc/init.d/sendmail restart