Linux Miscellany

Entitlements comparison – http://www.redhat.com/rhn/compare/#module

To reload inittab (following changes so the kernel is aware) without a reboot init q

Changing locales edit /etc/sysconfig/i18n

Documentation – /usr/share/doc/MAKEDEV/devices

Linux - GRUB

GRUB VGA modes

Colors(bits)	640×480	800×600	1024×768	1280×1024	1600×1200
256(8)	769	771	773	775	796
32768(15)	784	787	790	793	797
65536(16)	785	788	791	794	798
16,8M(24)	786	789	792	795	799

NOTE:

For normal kernels this is implemented by appending vga=<mode> (e.g vga=791) to the kernel line in grub.conf.

For XEN kernels the same is implemented by appending vga=gfx-<vesa mode> (e.g. vga=gfx-1024x768x16) to the kernel line in grub.conf

GRUB commands

displaymem - show system memory
boot - boot OS
root - sets and mount root partition
kernel - set kernel location and parameters
initrd - set initrd location
rootnotify - set root location, no mount

Kickstart

Consoles during text install:

tty1 = text install

tty2 = shell

tty3 = anaconda messages

tty4 = dmesg (as far as I can tell)

tty5 = disk messages (as far as I can tell)

RHEL Swap Recommendations

Recommended Swap Space for RHEL

The amount of swap recommended for RHEL depends on a number of factors including the amount of memory in the system and the workload imposed on that memory. The current guidelines for Red Hat Enterprise Linux swap space are as follows:

4GB of RAM requires a minimum of 2GB of swap space

4GB to 16GB RAM requires a minimum of 4GB of swap space

16GB to 64GB of RAM requires a minimum of 8GB of swap space

64GB to 256GB of RAM requires a minimum of 16GB of swap space

Multicast

To check if MULTICAST is enabled:

$ ifconfig (look for MULTICAST in output)

To enable MULTICAST routing:

# route add -net 224.0.0.0 netmask 240.0.0.0 dev bondN

Testing multicast

Copy swdepot:/software/linux/scripts/multicast.py to server(s)

On server(s) run multicast.py -h to get syntax

Start one server instance on one server and one client instance on another server

If multicast is working you will see output

Build Tricks

Error: unable to contact NFS server

For servers with multiple NICs eth0 may not be the correct one for the build as it may not be on the corporate network. For example, clustered servers, eth0 may be the heartbeat – all depending on how the server was cabled and ports configured.

You can get around this and find the “correct” NIC by editing the Kickstart file while running build.sh – simply change the network line. Instead of ”–device=eth0” replace with ”–device”. The kickstart process will stop and ask which device you want to use, you can scroll through the list until you find the one that works (a reboot is required following a failure).