10 boot time parameters you should know about the Linux kernel
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The Linux kernel accepts boot time parameters as it starts to boot system.
This is used to inform kernel about various hardware parameter. You need
boot time parameters:
* Troubleshoot system
* Hardware parameters that the kernel would not able to determine on its own
* Force kernel to override the default hardware parameters in order to
increase performance
* Password and other recovery operations
The kernel command line syntax
name=value1,value2,value3
Where,
- name : Keyword name, for example, init, ro, boot etc
Ten common Boot time parameters init
This sets the initial command to be executed by the kernel. Default is to
use /sbin/init, which is the parent of all processes.
To boot system without password pass /bin/bash or /bin/sh as argument to
init
init=/bin/bash
single
The most common argument that is passed to the init process is the word
'single' which instructs init to boot the computer in single user mode, and
not launch all the usual daemons
root=/dev/device
This argument tells the kernel what device (hard disk, floppy disk) to be
used as the root filesystem while booting. For example following boot
parameter use /dev/sda1 as the root file system:
root=/dev/sda1
If you copy entire partition from /dev/sda1 to /dev/sdb1 then use
root=/dev/sdb1
ro
This argument tells the kernel to mount root file system as read-only. This
is done so that fsck program can check and repair a Linux file system.
Please note that you should never ever run fsck on read/write file system.
rw
This argument tells the kernel to mount root file system as read and write
mode.
panic=SECOND
Specify kernel behavior on panic. By default, the kernel will not reboot
after a panic, but this option will cause a kernel reboot after N seconds.
For example following boot parameter will force to reboot Linux after 10
seconds
panic=10
maxcpus=NUMBER
Specify maximum number of processors that an SMP kernel should make use of.
For example if you have four cpus and would like to use 2 CPU then pass 2 as
a number to maxcpus (useful to test different software performances and
configurations).
maxcpus=2
debug
Enable kernel debugging. This option is useful for kernel hackers and
developers who wish to troubleshoot problem
selinux [0|1]
Disable or enable SELinux at boot time.
- Value 0 : Disable selinux
- Value 1 : Enable selinux
raid=/dev/mdN
This argument tells kernel howto assembly of RAID arrays at boot time.
Please note that When md is compiled into the kernel (not as module),
partitions of type 0xfd are scanned and automatically assembled into RAID
arrays. This autodetection may be suppressed with the kernel parameter
"raid=noautodetect". As of kernel 2.6.9, only drives with a type 0
superblock can be autodetected and run at boot time.
mem=MEMEORY_SIZE
This is a classic parameter. Force usage of a specific amount of memory to
be used when the kernel is not able to see the whole system memory or for
test. For example:
mem=1024M
The kernel command line is a null-terminated string currently up to 255
characters long, plus the final null. A string that is too long will be
automatically truncated by the kernel, a boot loader may allow a longer
command line to be passed to permit future kernels to extend this limit (H.
Peter Anvin ).
Other parameters initrd /boot/initrd.img
An initrd should be loaded. the boot process will load the kernel and an
initial ramdisk; then the kernel converts initrd into a "normal" ramdisk,
which is mounted read-write as root device; then /linuxrc is executed;
afterwards the "real" root file system is mounted, and the initrd file
system is moved over to /initrd; finally the usual boot sequence (e.g.
invocation of /sbin/init) is performed. initrd is used to provide/load
additional modules (device driver). For example, SCSI or RAID device driver
loaded using initrd.
hdX =noprobe
Do not probe for hdX drive. For example, disable hdb hard disk:
hdb=noprobe
If you disable hdb in BIOS, Linux will still detect it. This is the only way
to disable hdb.
ether=irq,iobase,[ARG1,ARG2],name
Where,
- ether: ETHERNET DEVICES
For example, following boot argument force probing for a second Ethernet
card (NIC), as the default is to only probe for one (irq=0,iobase=0 means
automatically detect them).
ether=0,0,eth1
How to begin the enter parameters mode?
You need to enter all this parameter at Grub or Lilo boot prompt. For
example if you are using Grub as a boot loader, at Grub prompt press 'e' to
edit command before booting.
1) Select second line
2) Again, press 'e' to edit selected command
3) Type any of above parameters.
--
Thanks & Regards
Sunil Naikwadi
9820668120
"Think positive in life always and look for opportunities when u can help
Others."
[Non-text portions of this message have been removed]
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