amavis - To allow only password protected archives

Add these two rules somewhere towards the end
of the list in $banned_filename_re:

# allow if it is or contains any undecipherable components:
[ qr'^UNDECIPHERABLE$'=> 0 ],

qr'^\.(zip|tar)$',  # block zip and tar (unless password protected)

Encrypting file in Linux

To encrypt single file, use command gpg

$ gpg -c filename

Enter Passphrase:
Repeat passphrase:

File becomes filename.gpg

To Decrypt

gpg filename.gpg
gpg: CAST5 encrypted data
gpg: Enter passphrase

original file is extracted out of the encrypted file

pwck, grpck

pwck for checking correctness of passwd file

grpck for checking correctness of group file

copy files by date

scp files created in DIR_NAME on a particular date to TARGET_COMPUTER

find DIR_NAME -mtime "{DATE}" -exec scp {} TARGET_COMPUTER \;

process states

use top command to know the status of a process

state of the process:
S-sleeping,
R-running,
T-stopped or traced,
D-uniterruptable sleep,
Z=zombie.

driver module for NIC card

Get full details of driver module for NIC card using "ethtool eth#

eth# could be eth0 or eth1 or eth2 ...

Enhanced mem support upto 64 GB

PAE is an Intel-provided memory address extension that enables support of
greater than 4 GB of physical memory upto 64 GB for most 32-bit (IA-32) Intel Pentium
Pro and later platforms.

Details at http://en.wikipedia.org/wiki/Physical_Address_Extension

To execute a PAE-enabled kernel add
swiotlb=force
to bootloader file grub.conf and reboot.