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 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 .
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.
Stage 3 - Load - The /boot/syslinux/ldlinux.sys will load the (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 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 (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 ( modules, excluding and ) require (library) modules to be present (https://wiki.syslinux.org/wiki/index.php/Common_Problems#ELF). The library modules and non-core modules should match the version of ldlinux.sys installed in the partition.

Installation on BIOS

Install the package.

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

After executing the script, do not forget to edit 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 script will install the bootloader code (usually to the VBR), copy 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 ; if you do not see a /boot mountpoint, mount it before you go any further.

Run with flags: (install the files), (mark the partition active with the boot flag), (install the MBR boot code): If this command fails with Syslinux BIOS install failed, the problem is likely that the binary could not find the partition containing /boot:

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

Now is the time to edit by following #Configuration and #Kernel parameters.

Manual install

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 mounted on /boot. For example, you can install Syslinux in the subdirectory:

# mkdir /boot/syslinux

Copy all files from 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.

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:

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: . 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 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 and the resulting 440 bytes are written to the MBR on device . Syslinux was installed on the first logical partition () 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 . To check:

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:
UEFI Syslinux does not support chainloading other EFI applications like or . Enhancement request:
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: , and
Memdisk is not available for UEFI. Enhancement request:

Installation on UEFI

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

Install the and packages. 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" --unicode

where is the partition containing the bootloader.

Create or edit by following #Configuration.

Configuration

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

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

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 to 0.

Configuration:

Text boot menu

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

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

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

Configuration:

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 COM32 module to your Syslinux folder:

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

Since version 5.00, additional 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 .

Configuration:

Since Syslinux 3.84, supports the directive. To use it, insert 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 HSHIFT $N and where 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:

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 directive in : for each 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 parameter needs to be replaced; see Persistent block device naming for supported methods.

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

Change to point to the correct root volume.

If you use dm-crypt encryption change the 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 line with . For example, where 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 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:

Auto boot

If you do not want to see the Syslinux menu at all, use the #Boot prompt, and set to 0 and comment out any menu entries. Setting the variable to 0 might also be a good idea. Make sure there is a DEFAULT set in your . Holding either or , or setting either or , 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 , use

MENU MASTER PASSWD passwd

to set a master bootloader password, and

MENU PASSWD passwd

within a 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, 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 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:

is the third partition on the first BIOS drive - drives are counted from zero, but partitions are counted from one.

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

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

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:

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

This may be required for booting from ISO images.

Chainloading other Linux systems

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 package.

The following instructions assume you have Syslinux installed already. These instructions will also assume that the typical Arch Linux configuration path of 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 . 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 .

# 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 . You can use the other Linux's bootloader menu file for reference. Below is an example:

And then add an entry to your main syslinux.cfg

Note that the other Linux entry in 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 .

Use this section to launch memtest:

HDT

HDT (Hardware Detection Tool) displays hardware information. Like before, the 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 and add the following to your configuration file:

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:

Clear menu

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

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.

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 and add:

See the Syslinux wiki for more details.

Hiding the menu

Use the option:

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

PXELINUX

PXELINUX is provided by the package.

For BIOS clients, copy the bootloader to the boot directory of the client. For version 5.00 and newer, also copy 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 configuration.

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

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 in with (or with ).

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 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 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 (the whole page might be relevant for troubleshooting too).

Using the Syslinux prompt

You can type in the name of the entry that you want to boot (as per your ). 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,

Create a temporary directory, in order to mount your root partition (if it does not exist already):
Mount under (in case is on the same partition, otherwise you will need to mount them both):
Edit again to suit your needs and save file.
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 and failing to read , 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 . If it starts at sector 1, you can move the partition(s) with 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 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 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 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 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 file. Hit to edit your boot parameters. Alternatively, press and type in the 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 with early modesetting, try to append the following in 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:

Replace the mbr code with the one your Windows drive has (details above), and append 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 in and use the default "command-line" prompt. It means:

avoid the directive
avoid
avoid ONERROR
avoid
use a higher
use
use

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

-DDEBUG_STDIO=1 -DCORE_DEBUG=1

Btrfs compression

Booting from btrfs with compression is not supported. 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. (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

gollark: Implicitly.

gollark: Wait, you basically just defined "sufficiently advanced" as "self-aware" here.

gollark: But consciousness doesn't necessarily depend on that anyway.

gollark: But if there was a version which could, it would probably need to model its own computing hardware, so actually maybe yes.

gollark: Practically speaking you run into the issue that Solomonoff induction can't be physically implemented.