Difference between revisions of "Syslinux"

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{{Note|Since Syslinux 4, Extlinux and Syslinux are the same thing.}}  
{{Note|Since Syslinux 4, Extlinux and Syslinux are the same thing.}}  
{{Note|Syslinux does not support [[UEFI]] as on May 2012. According to upstream, UEFI support will be eventually added to Syslinux, but there is no time-frame as to when it will be functional.}}
== Syslinux Boot Process ==
== Syslinux Boot Process ==

Revision as of 08:41, 23 May 2012

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Syslinux is a collection of boot loaders capable of booting from hard drives, CDs, and over the network via PXE. It supports the fat, ext2, ext3, ext4, and btrfs file systems.

Note: Since Syslinux 4, Extlinux and Syslinux are the same thing.
Note: Syslinux does not support UEFI as on May 2012. According to upstream, UEFI support will be eventually added to Syslinux, but there is no time-frame as to when it will be functional.

Syslinux Boot Process

At boot, the computer loads the MBR (/usr/lib/syslinux/mbr.bin). Then the MBR looks for the partition that is marked as active (boot flag). Once found, the volume boot record (VBR) will be executed. In the case of ext2/3/4 and fat12/16/32, the starting sector of ldlinux.sys is hard-coded into the VBR. The VBR will execute (ldlinux.sys). Therefore, if the location of ldlinux.sys changes, syslinux will no longer boot. In the case of btrfs, the above method will not work since files move around resulting in the sector location of ldlinux.sys changing. Therefore, the entire Syslinux code needs to be stored outside the filesystem. The code is stored in the sectors following the VBR. Once Syslinux is fully loaded, it looks for a configuration file, either extlinux.conf or syslinux.cfg. If one is found, the configuration file is loaded. If no configuration file is found, you will be given a syslinux prompt.


Automatic Install - syslinux

The syslinux-install_update script will install Syslinux, copy COM32 modules to /boot/syslinux, set the boot flag, and install the MBR. It can handle MBR and GPT disks along with softraid.

1. Install Syslinux

pacman -S syslinux

2. Make sure /boot is mounted
3. Run syslinux-install_update script -i (install) -a (set boot flag) -m (install mbr)

/usr/sbin/syslinux-install_update -iam

4. Edit /boot/syslinux/syslinux.cfg

Manual Install - syslinux

Note: If you are unsure of which partition table you are using (MBR or GPT), you are likely using the MBR partition table. Most of the time GPT will create a special MBR-style partition (type 0xEE) using the whole disk which will be displayed with the following command:
fdisk -l /dev/sda

or alternatively

sgdisk -l /dev/sda

will show " GPT: not present" if it is not a GPT disk.

Note: If you are trying to rescue an installed system with a live CD, be sure to chroot into it before executing these commands. If you do not chroot first, you must prepend all file paths (not /dev/ paths) with the mount point.

Make sure you have the syslinux package installed. Then install Syslinux onto your boot partition, which must contain a fat, ext2, ext3, ext4, or btrfs file system. You should install it on a mounted directory, not a /dev/sdXY device. You do not have to install it on the root directory of a file system, e.g., with device /dev/sda1 mounted on /boot you can install syslinux in the syslinux directory:

mkdir /boot/syslinux
extlinux --install /boot/syslinux 

MBR Partition Table

Next you need mark your boot partition active in your partition table. Applications capable of doing this include fdisk, cfdisk, sfdisk, (g)parted. It should look like this:

fdisk -l /dev/sda
  Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      104447       51200   83  Linux
/dev/sda2          104448   625142447   312519000   83  Linux

Install the master boot record:

dd bs=440 conv=notrunc count=1 if=/usr/lib/syslinux/mbr.bin of=/dev/sda

GUID Partition Table aka GPT

Main article GUID Partition Table.

Bit 2 of the attributes for the /boot partition need to be set.

sgdisk /dev/sda --attributes=1:set:2

This would toggle the attribute legacy BIOS bootable on partition 1


sgdisk /dev/sda --attributes=1:show
1:2:1 (legacy BIOS bootable)

Install the master boot record:

dd bs=440 conv=notrunc count=1 if=/usr/lib/syslinux/gptmbr.bin of=/dev/sda


When you reboot your system now, you will have a syslinux prompt. To automatically boot your system or get a boot menu, you still need to create a configuration file.

Configuring syslinux

The syslinux configuration file, syslinux.cfg, should be created in the same directory where you installed syslinux. In our case, '/boot/syslinux/'.

The bootloader will look for either syslinux.cfg (preferred) or extlinux.conf


  • Instead of LINUX, the keyword KERNEL can also be used. KERNEL tries to detect the type of the file, while LINUX always expects a Linux kernel.
  • TIMEOUT value is in units of 1/10 of a second.


Basic Syslinux Config

This is a simple configuration file that will show a boot: prompt and automatically boot after 5 seconds.



LABEL arch
        LINUX ../vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD ../initramfs-linux.img

LABEL archfallback
        LINUX ../vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD ../initramfs-linux-fallback.img

If you want to boot directly without seeing a prompt, set PROMPT to 0.

If you want to use UUID for persistent device naming instead of device names, change:

APPEND root=/dev/sda2 ro


APPEND root=UUID=<uuid here> ro

Text Boot menu

Syslinux also allows you to use a boot menu. To use it, copy the menu COM32 module to your syslinux directory:

cp /usr/lib/syslinux/menu.c32 /boot/syslinux/

If /boot is in the same partition as /usr, a symlink will also work:

ln -s /usr/lib/syslinux/menu.c32 /boot/syslinux/


UI menu.c32


LABEL arch
        MENU LABEL Arch Linux
        LINUX ../vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD ../initramfs-linux.img

LABEL archfallback
        MENU LABEL Arch Linux Fallback
        LINUX /vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD /initramfs-linux-fallback.img

For more details about the menu system, see http://git.kernel.org/?p=boot/syslinux/syslinux.git;a=blob;f=doc/menu.txt.

Graphical Boot menu

Syslinux also allows you to use a graphical boot menu. To use it, copy the vesamenu COM32 module to your syslinux folder:

cp /usr/lib/syslinux/vesamenu.c32 /boot/syslinux/

If /boot is the same partition as /, a symlink will also work:

ln -s /usr/lib/syslinux/vesamenu.c32 /boot/syslinux/

This config uses the same menu design as the Arch Install CD. The background file can be found there too.


UI vesamenu.c32


# Refer to http://www.syslinux.org/wiki/index.php/Comboot/menu.c32

MENU COLOR border       30;44   #40ffffff #a0000000 std
MENU COLOR title        1;36;44 #9033ccff #a0000000 std
MENU COLOR sel          7;37;40 #e0ffffff #20ffffff all
MENU COLOR unsel        37;44   #50ffffff #a0000000 std
MENU COLOR help         37;40   #c0ffffff #a0000000 std
MENU COLOR timeout_msg  37;40   #80ffffff #00000000 std
MENU COLOR timeout      1;37;40 #c0ffffff #00000000 std
MENU COLOR msg07        37;40   #90ffffff #a0000000 std
MENU COLOR tabmsg       31;40   #30ffffff #00000000 std

LABEL arch
        MENU LABEL Arch Linux
        LINUX ../vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD ../initramfs-linux.img

LABEL archfallback
        MENU LABEL Arch Linux Fallback
        LINUX ../vmlinuz-linux
        APPEND root=/dev/sda2 ro
        INITRD ../initramfs-linux-fallback.img

Since Syslinux 3.84, vesamenu.c32 supports the "MENU RESOLUTION $WIDTH $HEIGHT" directive. To use it, insert "MENU RESOLUTION 1440 900" into your config for a 1440x900 resolution. The background picture has to have exactly the right resolution, however, as syslinux will otherwise refuse to load the menu.


If you want to chainload other operating systems (such as Windows) or boot loaders, copy (or symlink) the chain.c32 module to the syslinux directory (for details, see the instructions in the previous section). Then create a section in the configuration file:

LABEL windows
        MENU LABEL Windows
        COM32 chain.c32
        APPEND hd0 3

hd0 3 is the third partition on the first BIOS drive - drives are counted from zero, but partitions are counted from one. For more details about chainloading, see [1].

If you have grub2 installed in your boot partition, you can chainload it by using:

LABEL grub2
       MENU LABEL Grub2
       COM32 chain.c32
       append file=../grub/boot.img

This may be required for booting from ISO images.

Using memtest

Use this LABEL section to launch memtest (install the memtest86+ package):

LABEL memtest
        MENU LABEL Memtest86+
        LINUX ../memtest86+/memtest.bin


HDT (Hardware Detection Tool) displays hardware information. Like before, the .c32 file has to be copied or symlinked from /boot/syslinux/. For PCI info, either copy or symlink /usr/share/hwdata/pci.ids to /boot/syslinux/pci.ids

        MENU LABEL Hardware Info
        COM32 hdt.c32

Reboot and power off

Use the following sections to reboot or power off your machine:

LABEL reboot
        MENU LABEL Reboot
        COM32 reboot.c32

LABEL poweroff
        MENU LABEL Power Off
        COMBOOT poweroff.com

Clear Menu

To clear the screen when exiting the menu, add the following line:



I have a Syslinux Prompt - Yikes!

You can type in the LABEL name of the entry that you want to boot (as per your syslinux.cfg). If you used the example configs, just type

boot: arch

If you get an error that the config file could not be loaded, you can pass your needed boot parameters, e.g.:

boot: ../vmlinuz-linux root=/dev/sda2 ro initrd=../initramfs-linux.img

If you do not have access to 'boot:' in ramfs, and therefore temporarily unable to boot kernel again,

1) create temp directory, in order to mount your root partition (if it does not exist already)

 mkdir -p /new_root

2) mount / under /new_root (in case /boot/ is on the same partition, otherwise you will need to mount them both) Note: if /boot is on its own ext2 partition then busybox cannot mount it.

 mount /dev/sd[a-z][1-9] /new_root

3) use 'vi' and edit syslinux.cfg again to suit your needs and save file;

4) reboot

No Default or UI found on some computers

Certain motherboard manufacturers have less compatibility for booting from USB devices than others. While an ext4 formatted USB drive may boot on a more recent computer, some computers may hang if the boot partition containing the kernel and initrd are not on a fat16 partition. To prevent an older machine from loading ldlinux and failing to read syslinux.cfg, use cfdisk to create a fat16 partition (<=2GB) and format with

pacman -S dosfstools
mkfs.msdos -F 16 /dev/sda1

then install and configure syslinux.

Windows boots up! No Syslinux!

Solution: Make sure the partition that contains /boot has the boot flag enabled. Also, make sure the boot flag is not enabled on the Windows partition. See the installation section above.

The MBR that comes with syslinux looks for the first active partition that has the boot flag set. The Windows partition was likely found first and had the boot flag set. If you wanted, you could use the MBR that Windows or MS-DOS fdisk provides.

Menu entries do nothing

You select a menu entry and it does nothing. It "refreshes" the menu.
This usually means that you have an error in your configuration. Hit Template:Keypress to edit your boot parameters. Alternatively, press Template:Keypress and type in the LABEL of your boot entry (Example: arch)

Cannot remove ldlinux.sys

ldlinux.sys has the immutable attribute set which prevents the file from being deleted or overwritten. This is because the sector location of the file must not change or else syslinux has to be reinstalled. To remove:

chattr -i /boot/syslinux/ldlinux.sys
rm /boot/syslinux/ldlinux.sys

A white block on the upper left corner appears when a kernel is loaded with modesetting on in early stage and when using vesamenu

Brain0 said: As of linux-3.0, the modesetting driver tries to keep the current contents of the screen after changing the resolution (at least it does so with my Intel, when having syslinux in text mode). It seems that this goes wrong when combined with the vesamenu module in syslinux (the white block is actually an attempt to keep the syslinux menu, but the driver fails to capture the picture from vesa graphics mode).

If you have a custom resolution and a vesamenu with early modesetting, try to append the following in the kernel line in syslinux.cfg to remove the white block and continue in graphics mode:

APPEND root=/dev/sda6 ro 5 radeon.modeset=1 vga=current logo.nologo quiet splash

See also