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5.2.3. /proc/cmdline

This file shows the parameters passed to the kernel at the time it is started. A sample /proc/cmdline file looks like the following: 
ro root=/dev/VolGroup00/LogVol00 rhgb quiet 3
This output tells us the following:
ro
The root device is mounted read-only at boot time. The presence of ro on the kernel boot line overrides any instances of rw.
root=/dev/VolGroup00/LogVol00
This tells us on which disk device or, in this case, on which logical volume, the root filesystem image is located. With our sample /proc/cmdline output, the root filesystem image is located on the first logical volume (LogVol00) of the first LVM volume group (VolGroup00). On a system not using Logical Volume Management, the root file system might be located on /dev/sda1 or /dev/sda2, meaning on either the first or second partition of the first SCSI or SATA disk drive, depending on whether we have a separate (preceding) boot or swap partition on that drive.
For more information on LVM used in Red Hat Enterprise Linux, refer to http://www.tldp.org/HOWTO/LVM-HOWTO/index.html.
rhgb
A short lowercase acronym that stands for Red Hat Graphical Boot, providing "rhgb" on the kernel command line signals that graphical booting is supported, assuming that /etc/inittab shows that the default runlevel is set to 5 with a line like this: 
id:5:initdefault:
quiet
Indicates that all verbose kernel messages except those which are extremely serious should be suppressed at boot time.