Configure Virtual Serial Port

1)      /etc/securetty  -append
ttyS0
ttyS1

2)      /etc/inittab  - uncomment and modify
S0:12345:respawn:/sbin/agetty -L 115200 ttyS0 vt100

3)      /boot/grub/menu.lst – modify the line of running kernel
root (hd0,0)
    kernel /vmlinuz-2.6.16.60-0.69.1-smp root=/dev/vg00/lvol1 vga=normal nomodeset 3 resume=/dev/vg00/lvol2 splash=silent showopts
crashkernel=256M@16M console=ttyS0,115200
    initrd /initrd-2.6.16.60-0.69.1-smp

Kdump memory requirement

---------------------------------------------------------------------------
    Configuring crashkernel on RHEL6.0 and RHEL6.1 kernels
---------------------------------------------------------------------------

Some mappings of ram and appropriate crashkernel values:

ram size        crashkernel parameter        ram / crashkernel factor
>0GB            128MB                        15
>2GB            256MB                        23
>6GB            512MB                        15
>8GB            768MB                        31

Linux Swapiness

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory and onto the swap disk. Because disks are much slower than RAM, this can lead to slower response times for system and applications if processes are too aggressively moved out of memory.

swappiness can have a value of between 0 and 100

swappiness=0 tells the kernel to avoid swapping processes out of physical memory for as long as possible
swappiness=100 tells the kernel to aggressively swap processes out of physical memory and move them to swap cache


The default setting in Linux is swappiness=60. Reducing the default value of swappiness will probably improve overall performance for a typical desktop installation. A value of swappiness=10 is recommended, but feel free to experiment.

To check the swappiness value use command: cat /proc/sys/vm/swappiness

To make a change permanent, edit the configuration file with your favorite editor:

vi /etc/sysctl.conf
and add following parameter to the end of the file like so:
vm.swappiness=10
Save the file and reboot.

System-wide File Descriptors (FD) Limits

Many application such as Oracle database or Apache web server needs this range quite higher. So you can increase the maximum number of open files by setting a new value in kernel variable /proc/sys/fs/file-max as follows (login as the root):
# sysctl -w fs.file-max=100000

Above command forces the limit to 100000 files. You need to edit /etc/sysctl.conf file and put following line so that after reboot the setting will remain as it is:
# vi /etc/sysctl.conf

Append a config directive as follows:
fs.file-max = 100000

Save and close the file. Users need to log out and log back in again to changes take effect or just type the following command:
# sysctl -p

Verify your settings with command:
# cat /proc/sys/fs/file-max

OR
# sysctl fs.file-max

1) Add the following line to /etc/security/limits.conf

webuser hard nofile 64000
then login as webuser

su - webuser
2) Edit following two files for webuser

append .bashrc and .bash_profile file by running

echo "ulimit -n 64000" >> .bashrc ; echo "ulimit -n 64000" >> .bash_profile
3) Log out, then log back in and verify that the changes have been made correctly:

$ ulimit -a | grep open
open files                      (-n) 64000