Syslinux

Syslinux is a collection of boot loaders capable of booting from drives, CDs, and over the network via PXE. Some of the supported file systems are FAT, NTFS, ext2, ext3, ext4, XFS, UFS/FFS, and uncompressed single-device Btrfs.

Warning: As of Syslinux 6.03, some of the features of the supported file systems are not supported by the bootloader. See [1] for more information.

Note: Syslinux, by itself, cannot access files from partitions other than its own. See #Chainloading on how to work around this.

BIOS Systems

Boot process overview

Stage 1 : Part 1 - Load MBR - At boot, the BIOS loads the 440 byte MBR boot code at the start of the disk (/usr/lib/syslinux/bios/mbr.bin or /usr/lib/syslinux/bios/gptmbr.bin).
Stage 1 : Part 2 - Search active partition. The Stage 1 MBR boot code looks for the partition that is marked as active (boot flag in MBR disks). Let us assume this is the /boot partition, for example.
Stage 2 : Part 1 - Execute volume boot record - The Stage 1 MBR boot code executes the Volume Boot Record (VBR) of the /boot partition. In the case of Syslinux, the VBR boot code is the starting sector of /boot/syslinux/ldlinux.sys which is created by the extlinux --install command. Note that ldlinux.sys is not the same as ldlinux.c32.
Stage 2 : Part 2 - Execute /boot/syslinux/ldlinux.sys - The VBR will load the rest of /boot/syslinux/ldlinux.sys. The sector location of /boot/syslinux/ldlinux.sys should not change, otherwise syslinux will not boot.
Note: In the case of Btrfs, the above method will not work since files move around resulting in changing of the sector location of ldlinux.sys. Therefore, in Btrfs the entire ldlinux.sys code is embedded in the space following the VBR and is not installed at /boot/syslinux/ldlinux.sys unlike the case of other filesystems.
Stage 3 - Load /boot/syslinux/ldlinux.c32 - The /boot/syslinux/ldlinux.sys will load the /boot/syslinux/ldlinux.c32 (core module) that contains the rest of the core part of syslinux that could not be fit into ldlinux.sys (due to file-size constraints). The ldlinux.c32 file should be present in every Syslinux installation and should match the version of ldlinux.sys installed in the partition. Otherwise Syslinux will fail to boot. See https://bugzilla.syslinux.org/show_bug.cgi?id=7 for more info.
Stage 4 - Search and Load configuration file - Once Syslinux is fully loaded, it looks for /boot/syslinux/syslinux.cfg (or /boot/syslinux/extlinux.conf in some cases) and loads it if it is found. If no configuration file is found, you will be dropped to a Syslinux boot: prompt. This step and the rest of non-core parts of Syslinux (/boot/syslinux/*.c32 modules, excluding lib*.c32 and ldlinux.c32) require /boot/syslinux/lib*.c32 (library) modules to be present (https://wiki.syslinux.org/wiki/index.php/Common_Problems#ELF). The lib*.c32 library modules and non-core *.c32 modules should match the version of ldlinux.sys installed in the partition.

Installation on BIOS

Install the syslinux package.

Note:

gptfdisk is required for GPT support following the #Automatic install section.
If your boot partition is FAT, you will also need mtools.

Installing the package is not the same as installing the bootloader. After installing the relevant package(s), the bootloader code itself needs to be installed (to the adequate area, usually the VBR) so to be able to boot the system; the following sections provide alternative instructions depending on the characteristics of your particular system.

Automatic install

Note: The syslinux-install_update script is Arch specific, and is not provided/supported by Syslinux upstream. Please direct any bug reports specific to the script to the Arch Bug Tracker and not upstream.

After executing the syslinux-install_update script, do not forget to edit /boot/syslinux/syslinux.cfg by following #Configuration and #Kernel parameters.

Warning: The syslinux-install_update script sets a default root partition that possibly will not match your particular system. It is important to point Syslinux to the correct root partition by editing /boot/syslinux/syslinux.cfg, or the OS will fail to boot. See #Kernel parameters.

The syslinux-install_update script will install the bootloader code (usually to the VBR), copy *.c32 modules to /boot/syslinux/, set the boot flag and install the boot code in the MBR. It can handle MBR and GPT disks along with software RAID:

If you use a separate boot partition, make sure that it is mounted. Check with lsblk; if you do not see a /boot mountpoint, mount it before you go any further.

Run syslinux-install_update with flags: -i (install the files), -a (mark the partition active with the boot flag), -m (install the MBR boot code):
```
# syslinux-install_update -i -a -m
```
If this command fails with Syslinux BIOS install failed, the problem is likely that the extlinux binary could not find the partition containing /boot:

# extlinux --install /boot/syslinux/

extlinux: cannot find device for path /boot/syslinux
extlinux: cannot open device (null)

This can happen, for example, when upgrading from LILO which, while booting a current custom kernel, turned a kernel command line parameter of say root=/dev/sda1 into its numeric equivalent root=801, as evidenced by /proc/cmdline and the output of the mount command. Remedy the situation by either continuing with the manual install described below while specifying --device=/dev/sda1 to extlinux, or simply by first rebooting into a stock Arch Linux kernel; its use of an initramfs avoids the problem.

Note:

If you rebooted your system now, you would get a Syslinux prompt. To automatically boot your system or get a boot menu, you need to create (edit) the configuration file.
If you are on another root directory (e.g. from an install disk) install SYSLINUX by directing to the chroot:

# syslinux-install_update -i -a -m -c /mnt

Now is the time to edit /boot/syslinux/syslinux.cfg by following #Configuration and #Kernel parameters.

Manual install

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.

Your boot partition, on which you plan to install Syslinux, must contain a FAT, ext2, ext3, ext4, or Btrfs file system. You do not have to install it on the root directory of a file system, e.g., with device /dev/sda1 mounted on /boot. For example, you can install Syslinux in the syslinux subdirectory:

# mkdir /boot/syslinux

Copy all .c32 files from /usr/lib/syslinux/bios/ to /boot/syslinux/ if you desire to use any menus or configurations other than a basic boot prompt. Do not symlink them.

# cp /usr/lib/syslinux/bios/*.c32 /boot/syslinux/

Now install the bootloader. For FAT, ext2/3/4, or btrfs boot partition use extlinux, where the device has been mounted:

# extlinux --install /boot/syslinux

Alternatively, for a FAT boot partition use syslinux, where the device is unmounted:

# syslinux --directory syslinux --install /dev/sda1

After this, proceed to install the Syslinux bootstrap code appropriate for the partition table:

mbr.bin will be installed for an #MBR partition table, or
gptmbr.bin will be installed for a #GUID partition table

as described in the next sections.

See Master Boot Record for further general information.

Tip: If you are unsure of which partition table you are using (MBR or GPT), you can check using blkid -s PTTYPE -o value /dev/sda.

Note: For a partitionless install, there is no need to install the Syslinux boot code to the MBR. You could skip below and jump to #Configuration. See [2].

MBR partition table

For an MBR partition table, ensure your boot partition is marked as "active" in your partition table (the "boot" flag is set). Applications capable of doing this include fdisk and 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 MBR:

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

An alternative MBR which Syslinux provides is: altmbr.bin. This MBR does not scan for bootable partitions; instead, the last byte of the MBR is set to a value indicating which partition to boot from. Here is an example of how altmbr.bin can be copied into position:

# printf '\x5' | cat /usr/lib/syslinux/bios/altmbr.bin - | dd bs=440 count=1 conv=notrunc iflag=fullblock of=/dev/sda

In this case, a single byte of value 5 (hexadecimal) is appended to the contents of altmbr.bin and the resulting 440 bytes are written to the MBR on device sda. Syslinux was installed on the first logical partition (/dev/sda5) of the disk.

GUID partition table

For a GPT, ensure that attribute bit 2 "Legacy BIOS bootable" is set for the /boot partition. For Parted it can be set using the "legacy_boot" flag. Using sgdisk the command to set the attribute is:

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

This will set the attribute "legacy BIOS bootable" on partition 1 of /dev/sda. To check:

# sgdisk /dev/sda --attributes=1:show

1:2:1 (legacy BIOS bootable)

Install the MBR:

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

UEFI Systems

Note:

efi64 denotes x86_64 UEFI systems, for IA32 (32-bit) EFI replace efi64 with efi32 in the below commands.
For Syslinux, the kernel and initramfs files need to be in the EFI system partition (aka ESP), as Syslinux does not (currently) have the ability to access files outside its own partition (i.e. outside ESP in this case). For this reason, it is recommended to mount ESP at /boot.
The automatic install script /usr/bin/syslinux-install_update does not support UEFI install.
The configuration syntax of syslinux.cfg for UEFI is same as that of BIOS.

Limitations of UEFI Syslinux

Using TAB to edit kernel parameters in UEFI Syslinux menu might lead to garbaged display (text on top of one another). Bug report: [3]
UEFI Syslinux does not support chainloading other EFI applications like UEFI Shell or Windows Boot Manager. Enhancement request: [4]
In some cases, UEFI Syslinux might not boot in some Virtual Machines like QEMU/OVMF or VirtualBox or some VMware products/versions and in some UEFI emulation environments like DUET. A Syslinux contributor has confirmed no such issues present on VMware Workstation 10.0.2 and Syslinux-6.02 or later. Bug reports: [5], [6] and [7]
Memdisk is not available for UEFI. Enhancement request: [8]

Installation on UEFI

Note: In the commands related to UEFI, esp denotes the mountpoint of the EFI system partition aka ESP.

Install the syslinux and efibootmgr packages from the official repositories. Then setup Syslinux in the ESP as follows:
Copy Syslinux files to ESP:

# mkdir -p esp/EFI/syslinux
# cp -r /usr/lib/syslinux/efi64/* esp/EFI/syslinux

Setup boot entry for Syslinux using efibootmgr:

# efibootmgr --create --disk /dev/sdX --part Y --loader /EFI/syslinux/syslinux.efi --label "Syslinux" --verbose

where /dev/sdXY is the partition containing the bootloader.

Create or edit esp/EFI/syslinux/syslinux.cfg by following #Configuration.

Note:

The configuration file for UEFI is esp/EFI/syslinux/syslinux.cfg, not /boot/syslinux/syslinux.cfg. Files in /boot/syslinux/ are BIOS specific and not related to UEFI Syslinux.
When booted in BIOS mode, efibootmgr will not be able to set EFI nvram entry for /EFI/syslinux/syslinux.efi. To work around, place resources at the default EFI location: esp/EFI/syslinux/* -> esp/EFI/BOOT/* and esp/EFI/syslinux/syslinux.efi -> esp/EFI/BOOT/bootx64.efi

Configuration

The Syslinux configuration file, syslinux.cfg, should be created in the same directory where you installed Syslinux. In our case, /boot/syslinux/ for BIOS systems and esp/EFI/syslinux/ for UEFI systems.

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

Tip:

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 0.1 seconds.

Examples

Note:

Any configuration file found in the examples needs to be edited to set the proper kernel parameters. See section #Kernel parameters.
Please, pay close attention to the paths. The examples may not be suitable for your installation, especially when using UEFI.
The following examples assume that the kernel and initrd files are located one directory level up in relation to the location of syslinux.cfg (or, more precisely, one level up from the working directory).

Boot prompt

This is a simple configuration file that will show a boot: prompt and will automatically boot after 5 seconds. If you want to boot directly without seeing a prompt, set PROMPT to 0.

Configuration:

* BIOS: /boot/syslinux/syslinux.cfg
* UEFI: esp/EFI/syslinux/syslinux.cfg

PROMPT 1
TIMEOUT 50
DEFAULT arch

LABEL arch
	LINUX ../vmlinuz-linux
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	INITRD ../initramfs-linux.img

LABEL archfallback
	LINUX ../vmlinuz-linux
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	INITRD ../initramfs-linux-fallback.img

Text boot menu

Syslinux also allows you to use a boot menu. To use it, copy the menu and libutil modules to your Syslinux directory:

# cp /usr/lib/syslinux/bios/{menu,libutil}.c32 /boot/syslinux/

Since version 5.00, additional lib*.c32 library modules are frequently needed too. See the Syslinux wiki for the module dependency tree.

Configuration:

* BIOS: /boot/syslinux/syslinux.cfg
* UEFI: esp/EFI/syslinux/syslinux.cfg

UI menu.c32
PROMPT 0

MENU TITLE Boot Menu
TIMEOUT 50
DEFAULT arch

LABEL arch
	MENU LABEL Arch Linux
	LINUX ../vmlinuz-linux
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	INITRD ../initramfs-linux.img

LABEL archfallback
	MENU LABEL Arch Linux Fallback
	LINUX ../vmlinuz-linux
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	INITRD ../initramfs-linux-fallback.img

For more details about the menu system, see the Syslinux wiki.

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/bios/vesamenu.c32 /boot/syslinux/

Since version 5.00, additional lib*.c32 library modules are frequently needed too. See the Syslinux wiki for the module dependency tree.

Note: If you are using UEFI, make sure to copy from /usr/lib/syslinux/efi64/ (or efi32 for IA32 (32-bit) EFI systems), otherwise you will be presented with a black screen. In that case, boot from a live medium and use chroot to make the appropriate changes.

This configuration uses the same menu design as the Arch Install CD, its configuration can be found at gitlab.archlinux.org. The Arch Linux background image can be downloaded from there, too. Copy the image to /boot/syslinux/splash.png.

Configuration:

* BIOS: /boot/syslinux/syslinux.cfg
* UEFI: esp/EFI/syslinux/syslinux.cfg

UI vesamenu.c32
DEFAULT arch
PROMPT 0
MENU TITLE Boot Menu
MENU BACKGROUND splash.png
TIMEOUT 50

MENU WIDTH 78
MENU MARGIN 4
MENU ROWS 5
MENU VSHIFT 10
MENU TIMEOUTROW 13
MENU TABMSGROW 11
MENU CMDLINEROW 11
MENU HELPMSGROW 16
MENU HELPMSGENDROW 29

# Refer to https://wiki.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=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	INITRD ../initramfs-linux.img


LABEL archfallback
	MENU LABEL Arch Linux Fallback
	LINUX ../vmlinuz-linux
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw
	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 configuration for a 1440x900 resolution. However, the background picture has to have exactly the right resolution, as Syslinux will otherwise refuse to load the menu.

To center the menu and adjust resolution, use MENU RESOLUTION, MENU HSHIFT $N and MENU VSHIFT $N where $N is a positive number. The default values are both 0 which is the upper-left hand corner of your monitor. Conversely, a negative number starts from the opposite end of the screen (e.g. VHSHIFT -4 would be 4 rows from the bottom of the screen).

To move the menu to the center, add or edit these values:

* BIOS: /boot/syslinux/syslinux.cfg
* UEFI: esp/EFI/syslinux/syslinux.cfg

MENU RESOLUTION 800 600 # or whatever your screen resolution is
MENU WIDTH 78           # width of the menu also required to bring the menu box to size
MENU VSHIFT 10          # moves menu down
MENU HSHIFT 10          # moves menu right

VESA standards are commonly a maximum of 25 rows and 80 columns, so going higher than those values might move the menu off the screen, potentially requiring editing from a rescue CD.

Kernel parameters

The kernel parameters are set by using the APPEND directive in syslinux.cfg: for each LABEL entry, a maximum of one APPEND line is accepted (i.e. spanning multiple lines is not valid).

It is recommended to make the following changes for the "fallback" entry as well.

In the simplest case, the value of the root parameter needs to be replaced; see Persistent block device naming for supported methods.

 APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw

Change root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX to point to the correct root volume.

If you use dm-crypt encryption change the APPEND line to use your encrypted volume:

APPEND root=/dev/mapper/name cryptdevice=UUID=YYYYYYYY-YYYY-YYYY-YYYY-YYYYYYYYYYYY:name rw

If booting a btrfs subvolume, amend the APPEND line with rootflags=subvol=<root subvolume>. For example, where /dev/disk/by-uuid/XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX has been mounted as a btrfs subvolume called 'ROOT' (e.g. mount -o noatime,subvol=ROOT /dev/disk/by-uuid/XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX /mnt), then the APPEND line would need to be modified as follows:

APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw rootflags=subvol=ROOT

A failure to do so will otherwise result in the following error message: ERROR: Root device mounted successfully, but /sbin/init does not exist.

Auto boot

If you do not want to see the Syslinux menu at all, use the #Boot prompt, and set PROMPT to 0 and comment out any UI menu entries. Setting the TIMEOUT variable to 0 might also be a good idea. Make sure there is a DEFAULT set in your syslinux.cfg. Holding either Shift or Alt, or setting either Caps Lock or Scroll Lock, during boot will allow for options other than default to be used. See the upstream wiki for additional alternatives.

Security

Syslinux has two levels of bootloader security: a menu master password, and a per-menu-item password. In syslinux.cfg, use

MENU MASTER PASSWD passwd

to set a master bootloader password, and

MENU PASSWD passwd

within a LABEL block to password-protect individual boot items.

The passwd can be either a cleartext password or hashed: see official documentation.

Chainloading

Syslinux BIOS cannot directly chainload files located on other partitions; however, chain.c32 can boot a partition boot sector (VBR) or another disk's MBR.

Chainloading a partition's VBR

If you want to chainload other operating systems (such as Windows) or boot loaders, copy the chain.c32 module to the Syslinux directory (additional lib*.c32 library modules might be needed too; for details, see the instructions in the previous section). Then create a section in the configuration file:

/boot/syslinux/syslinux.cfg

...
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.

Note: For Windows, this skips the system's own boot manager (bootmgr), which is required for a few important updates (eg.) to complete. In such cases it may be advisable to temporarily set the MBR boot flag to the Windows partition (eg. with GParted), let the update finish installing, and then reset the flag to the Syslinux partition (eg. with Windows's own DiskPart).

Chainloading a disk's MBR

If you are unsure about which drive your BIOS thinks is "first", you can instead use the MBR identifier, or if you are using GPT, the filesystem labels. To use the MBR identifier, run the command

# fdisk -l /dev/sdb

Disk /dev/sdb: 128.0 GB, 128035676160 bytes 
255 heads, 63 sectors/track, 15566 cylinders, total 250069680 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xf00f1fd3
 
Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152    7  HPFS/NTFS/exFAT
/dev/sdb2         4196352   250066943   122935296    7  HPFS/NTFS/exFAT

replacing /dev/sdb with the drive you wish to chainload. Using the hexadecimal number under Disk identifier: 0xf00f1fd3 in this case, the syntax in syslinux.cfg is

/boot/syslinux/syslinux.cfg

...
LABEL windows
	MENU LABEL Windows
	COM32 chain.c32
	APPEND mbr:0xf00f1fd3
...

For more details about chainloading, see the Syslinux wiki.

Chainloading other boot loaders

If you have GRUB installed on the same partition, you can chainload it by using:

/boot/syslinux/syslinux.cfg

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

Alternatively, it is also possible to load GRUB as a linux kernel by prepending lnxboot.img to core.img. The file lnxboot.img is part of core/grub and can be found in /usr/lib/grub/i386-pc.

/boot/syslinux/syslinux.cfg

...
LABEL grub2lnx
	MENU LABEL Grub2 (lnxboot)
	LINUX ../grub/i386-pc/lnxboot.img
	INITRD ../grub/i386-pc/core.img
...

This may be required for booting from ISO images.

Chainloading other Linux systems

The factual accuracy of this article or section is disputed.

Reason: Among other inaccuracies... 1_ There is no obligation to install yet another boot loader if you already have one related to the other partition/OS (e.g. GRUB2 installed in the MBR or in the VBR of the partition being chainloaded to). 2_ Syslinux (in any of its derivatives) is never "installed to the MBR", so mentioning the MBR in this section without any explanation of what it is being meant or how to do it in practical terms is just adding confusion. 3_ Typos and misspelling. 4_No need to explain (yet again) how to install some (other) bootloader to some (other) partition / OS; just how to chainload from Syslinux to that other partition / bootloader / OS. (Discuss in Talk:Syslinux)

Chainloading another bootloader such as Windows' is pretty obvious, as there is a definite bootloader to chain to. But with Syslinux, it is only able to load files residing on the same partition as the configuration file. Thus, if you have another version of Linux on a separate partition, without a shared /boot, it becomes necessary to employ EXTLINUX rather than the other OS's default bootloader (eg. GRUB2). Essentially, EXTLINUX can be installed on the partition superblock/VBR and be called as a separate bootloader right from the MBR installed by Syslinux. EXTLINUX is part of The Syslinux Project and is included with the syslinux package.

The following instructions assume you have Syslinux installed already. These instructions will also assume that the typical Arch Linux configuration path of /boot/syslinux is being used and the chainloaded system's / is on /dev/sda3.

From a booted Linux (likely the partition that Syslinux is set up to boot), mount the other system's root partition to your desired mount point. In this example this will be /mnt. Also, if a separate /boot partition is used on the second operating system, that will also need to be mounted. The example assumes this is /dev/sda2.

# mount /dev/sda3 /mnt
# mount /dev/sda2 /mnt/boot (only necessary for separate /boot)

Install EXTLINUX to the partition VBR, and copy necessary *.c32 files

# extlinux -i /mnt/boot/syslinux/ (first create the directory if necessary)
# cp /usr/lib/syslinux/bios/*.c32 /mnt/boot/syslinux

Create /mnt/boot/syslinux/syslinux.cfg. You can use the other Linux's bootloader menu file for reference. Below is an example:

/mnt/boot/syslinux/syslinux.cfg on /dev/sda3

TIMEOUT 10

UI menu.c32

LABEL OtherLinux
	LINUX /boot/vmlinuz-linux
	INITRD /boot/initramfs-linux.img
	APPEND root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw quiet

LABEL MAIN
	COM32 chain.c32
	APPEND hd0 0

And then add an entry to your main syslinux.cfg

/boot/syslinux/syslinux.cfg

LABEL OtherLinux
	COM32 chain.c32
	APPEND hd0 3

Note that the other Linux entry in <other-OS>/boot/syslinux/syslinux.cfg will need to be edited each time you update this OS's kernel unless it has symlinks to its latest kernel and initrd in /. Since we are booting the kernel directly and not chainloading the other-OS's default bootloader.

Using memtest

Install memtest86+ from the official repositories.

Use this LABEL section to launch memtest:

/boot/syslinux/syslinux.cfg

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

Note: If you are using PXELINUX, change the name from memtest.bin to memtest since PXELINUX treats the file with .bin extension as a boot sector and loads only 2KB of it.

HDT

HDT (Hardware Detection Tool) displays hardware information. Like before, the .c32 file has to be copied from /boot/syslinux/. Additional lib*.c32 library modules might be needed too. For PCI info, copy /usr/share/hwdata/pci.ids to /boot/syslinux/pci.ids and add the following to your configuration file:

/boot/syslinux/syslinux.cfg

LABEL hdt
	MENU LABEL Hardware Info
	COM32 hdt.c32

Reboot and power off

Note: As of Syslinux 6.03, poweroff.c32 only works with APM and not with ACPI. For a possible solution, see acpioff: COM32 module to shut off machine using ACPI.

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

/boot/syslinux/syslinux.cfg

LABEL reboot
	MENU LABEL Reboot
	COM32 reboot.c32

LABEL poweroff
	MENU LABEL Power Off
	COM32 poweroff.c32

Clear menu

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

/boot/syslinux/syslinux.cfg

MENU CLEAR

Keyboard layout

If you often have to edit your boot command with diverse parameters in the Syslinux boot prompt, then you might want to remap your keyboard layout. This allows you to enter "=", "/" and other characters easily on a non-US keyboard.

Note: keytab-lilo, which is included in the syslinux package, is a perl script invoking the loadkeys program.

To create a compatible keymap (e.g. a german one) run:

# keytab-lilo /usr/share/kbd/keymaps/i386/qwerty/us.map.gz /usr/share/kbd/keymaps/i386/qwertz/de.map.gz > /boot/syslinux/de.ktl

Now edit syslinux.cfg and add:

/boot/syslinux/syslinux.cfg

KBDMAP de.ktl

See the Syslinux wiki for more details.

Hiding the menu

Use the option:

/boot/syslinux/syslinux.cfg

MENU HIDDEN

to hide the menu while displaying only the timeout. Press any key to bring up the menu.

PXELINUX

Note: For UEFI, Syslinux uses the same binary for disk booting and network booting. Loading files from TFTP or other network protocols will require network booting Syslinux.

PXELINUX is provided by the syslinux package.

For BIOS clients, copy the {l,}pxelinux.0 bootloader to the boot directory of the client. For version 5.00 and newer, also copy ldlinux.c32 from the same package:

# cp /usr/lib/syslinux/bios/pxelinux.0 "TFTP_root/boot/"
# cp /usr/lib/syslinux/bios/ldlinux.c32 "TFTP_root/boot/"
# mkdir "TFTP_root/boot/pxelinux.cfg"

We also created the pxelinux.cfg directory, which is where PXELINUX searches for configuration files by default. Because we do not want to discriminate between different host MACs, we then create the default configuration.

TFTP_root/boot/pxelinux.cfg/default

DEFAULT linux

LABEL linux
	KERNEL vmlinuz-linux
	APPEND initrd=initramfs-linux.img quiet ip=:::::eth0:dhcp nfsroot=10.0.0.1:/arch

Or if you are using NBD, use the following append line:

append ro initrd=initramfs-linux.img ip=:::::eth0:dhcp nbd_host=10.0.0.1 nbd_port=10809 nbd_name=arch root=/dev/nbd0

Note: You will need to change nbd_host and/or nfsroot, respectively, to match your network configuration (the address of the NFS/NBD server)

PXELINUX uses the same configuration syntax as SYSLINUX; refer to the upstream documentation for more information.

The kernel and initramfs will be transferred via TFTP, so the paths to those are going to be relative to the TFTP root. Otherwise, the root filesystem is going to be the NFS mount itself, so those are relative to the root of the NFS server.

To actually load PXELINUX, replace filename "/grub/i386-pc/core.0"; in /etc/dhcpd.conf with filename "/pxelinux.0" (or with filename "/lpxelinux.0").

Booting ISO9660 image files with memdisk

Syslinux supports booting from ISO images directly using the memdisk module, see Multiboot USB drive#Using Syslinux and memdisk for examples.

Serial console

See Working with the serial console#Syslinux.

Boot another OS once

It is possible to temporarily change the default Syslinux action and boot another label only during the next boot. The following command shows how to boot the archfallback label once:

# extlinux -o archfallback /boot/syslinux

During the next boot, the specified label will be booted without any Syslinux prompt showing up. The default Syslinux boot behaviour will be restored on the next reboot.

Troubleshooting

Failed to load ldlinux

An error message such as "Failed to load ldlinux.c32" during the initial boot can be triggered by many diverse reasons. One potential reason could be a change in file system tools or in a file system structure, depending on its own version.

Warning: As of Syslinux 6.03, some of the features of the supported file systems are not supported by the bootloader. See [9] for more information.

Note: There is no direct and unique correspondence between a message such as Failed to load ldlinux.c32 and a problem related to the file system:

Other alternative symptoms, instead of this message, could also indicate a problem related to the file system.
The message does not necessarily mean that the problem is related to the file system; there are other possible reasons for this type of messages.

See also [10] (the whole page might be relevant for troubleshooting too).

Using the Syslinux prompt

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 configurations, just type:

boot: arch

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

boot: ../vmlinuz-linux root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw initrd=../initramfs-linux.img

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

1. Create a temporary 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: Busybox cannot mount /boot if it is on its own ext2 partition.

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

3. Use vim and edit syslinux.cfg again to suit your needs and save file.

4. Reboot.

Fsck fails on root partition

In the case of a badly corrupted root partition (in which the journal is damaged), in the ramfs emergency shell, mount the root file system:

# mount /dev/root partition /new_root

And grab the tune2fs binary from the root partition (it is not included in Syslinux):

# cp /new_root/sbin/tune2fs /sbin/

Follow the instructions at ext2fs: no external journal to create a new journal for the root partition.

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, create a partition (≤ 2 GB) and format to FAT16 using dosfstools:

# mkfs.fat -F 16 /dev/sda1

then install and configure Syslinux.

Missing operating system

Check that you have installed gptmbr.bin for GPT and mbr.bin for MBR partition table. A "Missing operating system" message comes from mbr.bin while gptmbr.bin would show a "Missing OS" message.
Check whether the partition that contains /boot has the "boot" flag enabled.
Check whether the first partition at the boot device starts at sector 1 rather than sector 63 or 2048. Check this with fdisk -l. If it starts at sector 1, you can move the partition(s) with gparted from a rescue disk. Or, if you have a separate boot partition, you can back up /boot with

# cp -a /boot /boot.bak

and then boot up with the Arch install disk. Next, use cfdisk to delete the /boot partition, and recreate it. This time it should begin at the proper sector, 63. Now mount your partitions and chroot into your mounted system, as described in the installation guide. Restore /boot with the command

# cp -a /boot.bak/ /boot/

Check if /etc/fstab is correct, run:

# syslinux-install_update -iam

and reboot.

You will also get this error if you are trying to boot from a md RAID 1 array and created the array with a too new version of the metadata that Syslinux does not understand. As of August 2013 by default mdadm will create an array with version 1.2 metadata, but Syslinux does not understand metadata newer than 1.0. If this is the case you will need to recreate your RAID array using the --metadata=1.0 flag to mdadm.

Windows boots up, ignoring 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 just "refreshes" the menu. This usually means that you have an error in your syslinux.cfg file. Hit Tab to edit your boot parameters. Alternatively, press Esc and type in the LABEL of your boot entry (e.g. arch). Another cause could be that you do not have a kernel installed. Find a way to access your file system (through live CD, etc) and make sure that /mount/vmlinuz-linux exists and does not have a size of 0. If this is the case, reinstall your kernel.

Cannot remove ldlinux.sys

The ldlinux.sys file has the immutable attribute set, which prevents it 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 it, run:

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

White block in upper left corner when using vesamenu

Problem: 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 syslinux.cfg to remove the white block and continue in graphics mode:

APPEND root=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw 5 vga=current quiet splash

Chainloading Windows does not work, when it is installed on another drive

If Windows is installed on a different drive than Arch and you have trouble chainloading it, try the following configuration:

LABEL Windows
	MENU LABEL Windows
	COM32 chain.c32
	APPEND mbr:0xdfc1ba9e swap

Replace the mbr code with the one your Windows drive has (details above), and append swap to the options.

Read bootloader log

In some cases (e.g. bootloader unable to boot kernel) it is highly desirable to get more information from the boot process. Syslinux prints error messages to screen but the boot menu quickly overwrites the text. To avoid losing the log information, disable UI menu in syslinux.cfg and use the default "command-line" prompt. It means:

avoid the UI directive
avoid ONTIMEOUT
avoid ONERROR
avoid MENU CLEAR
use a higher TIMEOUT
use PROMPT 1
use DEFAULT problematic_label

To get more detailed debug log, recompile the syslinux package with additional CFLAGS:

-DDEBUG_STDIO=1 -DCORE_DEBUG=1

Btrfs compression

Booting from btrfs with compression is not supported.[11] This error will show:

btrfs: found compressed data, cannot continue!
invalid or corrupt kernel image.

Btrfs multi-device

Booting from multiple-device btrfs is not supported.[12] (As of 21-Jul-2016 line 1246 in validate_device_btrfs() in main.c) This head-scratching error will show (assuming you are installing on sda1):

/boot/syslinux is device /dev/sda1
extlinux: path /boot/syslinux doesn't match device /dev/sda1