As Debian big fan, sometime I found that apt-get update command reveal this error:
“E: Some index files failed to download. They have been ignored, or old ones used instead.”

This command is very simple solution I found:

# rm /var/lib/apt/lists/partial/*

After that, apt-get update && apt-get upgrade command should be fine.

Source:
– http://forums.debian.net/viewtopic.php?f=10&t=108618

/boot Partition in CentOS 6 can be cleaned by removing old kernels.

These are the steps:

1. Check /boot partition (98% used)

# df -h
Filesystem      Size  Used Avail Use% Mounted on
...
/dev/sda1        93M   86M  2.1M  98% /boot
...

2. Check installed kernel

# rpm -q kernel
kernel-2.6.32-431.el6.x86_64
kernel-2.6.32-431.29.2.el6.x86_64
kernel-2.6.32-504.1.3.el6.x86_64

3. Install package-cleanup

# yum install yum-utils
# package-cleanup --oldkernels --count=2
=======================================================================================================================================
 Package              Arch                 Version                        Repository                                              Size
=======================================================================================================================================
Removing:
 kernel               x86_64               2.6.32-431.el6                 @anaconda-CentOS-201311272149.x86_64/6.5               121 M

Transaction Summary
=======================================================================================================================================
Remove        1 Package(s)

Installed size: 121 M
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Erasing    : kernel-2.6.32-431.el6.x86_64                                                                                        1/1 
  Verifying  : kernel-2.6.32-431.el6.x86_64                                                                                        1/1 

Removed:
  kernel.x86_64 0:2.6.32-431.el6                                                                                                       

Complete!

4. Check /boot partition (67% used)

# df -h
Filesystem      Size  Used Avail Use% Mounted on
...
/dev/sda1        93M   59M   30M  67% /boot
...

5. Limit only 2 latest kernel for later updates

# vim /etc/yum.conf
   ...[edit yum.conf]...
   installonly_limit=2
   ...[edit yum.conf]...

Source:
– http://www.if-not-true-then-false.com/2012/delete-remove-old-kernels-on-fedora-centos-red-hat-rhel/

Having several Linux Servers, SSH access is mandatory communication between me and those servers. These are several tips for SSH Server administration that save the day:

Add these line on /etc/ssh/sshd_config:

• Allow only specific user (never use root login for remote SSH access)

  AllowUsers username
  DenyUsers All

• Disable DNS and GSSAPI (solving slow login respond, especially from private network)

  UseDNS no
  GSSAPIAuthentication no

Make sure to restart SSH service after changing sshd_config:

# service ssh restart

or

# /etc/init.d/ssh restart

Additional tip:

• Add this options on /etc/resolv.conf (solving slow login respond on RHEL/CentOS)
  

options single-request-reopen

Source:

– http://injustfiveminutes.com/2013/03/13/fixing-ssh-login-long-delay/