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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:
The root device is mounted read-only at boot time. The presence of ro on the kernel boot line overrides any instances of rw.
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
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:
Indicates that all verbose kernel messages except those which are extremely serious should be suppressed at boot time.