Difference between revisions of "Syslinux"

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m (→‎Installation: Use upper case for the bootloader variants of the Syslinux family.)
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First you have to create a compatible keymap, in this example German:
First you have to create a compatible keymap, in this example German:
{{Note|{{ic|us.kmap}} needs to be created or the following won't work.}}
{{Note|{{ic|us.kmap}} needs to be created or the following will not work.}}
  $ cp /usr/share/kbd/keymaps/i386/qwertz/de.map.gz .
  $ cp /usr/share/kbd/keymaps/i386/qwertz/de.map.gz .
  $ cp /usr/share/kbd/keymaps/i386/qwerty/us.map.gz .
  $ cp /usr/share/kbd/keymaps/i386/qwerty/us.map.gz .
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=== Missing operating system ===
=== Missing operating system ===
* Check that you've installed {{ic|gptmbr.bin}} for GPT partition table and {{ic|mbr.bin}} for DOS partition table. "Missing operating system" message comes from {{ic|mbr.bin}} while {{ic|gptmbr.bin}} has message "Missing OS".
* Check that you have installed {{ic|gptmbr.bin}} for GPT partition table and {{ic|mbr.bin}} for DOS partition table. "Missing operating system" message comes from {{ic|mbr.bin}} while {{ic|gptmbr.bin}} has message "Missing OS".
* Check if the partition that contains {{ic|/boot}} has the boot flag enabled.
* Check if the partition that contains {{ic|/boot}} has the boot flag enabled.
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=== Menu entries do nothing ===
=== 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 {{ic|syslinux.cfg}} file. Hit {{ic|Tab}} to edit your boot parameters. Alternatively, press {{ic|Esc}} and type in the {{ic|LABEL}} of your boot entry (e.g. ''arch''). Another cause could be that you don't have a kernel installed. Find a way to access your file system (through live CD, etc) and make sure that {{ic|/mount/vmlinuz-linux}} exists and doesn't have a size of 0. If this is the case, [[Kernel_Panics#Option_2:_Reinstall_kernel|reinstall your kernel]].
You select a menu entry and it does nothing, it just ''"refreshes"'' the menu. This usually means that you have an error in your {{ic|syslinux.cfg}} file. Hit {{ic|Tab}} to edit your boot parameters. Alternatively, press {{ic|Esc}} and type in the {{ic|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 {{ic|/mount/vmlinuz-linux}} exists and does not have a size of 0. If this is the case, [[Kernel_Panics#Option_2:_Reinstall_kernel|reinstall your kernel]].
=== Cannot remove ldlinux.sys ===
=== Cannot remove ldlinux.sys ===

Revision as of 07:53, 28 April 2015


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: Syslinux cannot access files from partitions other than its own. For an alternative bootloader with the multi-fs feature see GRUB.

BIOS Systems

Boot process overview

  1. 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).
  2. 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.
  3. 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 ldlinux.sys is not same as ldlinux.c32.
  4. Stage 2 : Part 2 - Execute /boot/syslinux/ldlinux.sys - The VBR will load 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.
  5. 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 core part of syslinux that could not be fit into ldlinux.sys (due to file-size constraints). The ldlinux.c32 should be present in every syslinux/extlinux installation and should match the version of ldlinux.sys installed in the partition. Otherwise syslinux will fail to boot. See http://bugzilla.syslinux.org/show_bug.cgi?id=7 for more info.
  6. 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 rest of non-core part of syslinux (/boot/syslinux/*.c32 modules, excluding lib*.c32 and ldlinux.c32) require /boot/syslinux/lib*.c32 (library) modules to be present (http://www.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.


Install the syslinux package from the official repositories.

  • Since Syslinux 4, EXTLINUX and SYSLINUX are the same thing.
  • gptfdisk is required for GPT support using the automated script.
  • If your boot partition is FAT, you will also need mtools.

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 create or 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 Syslinux, 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.

  • 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.
  • If you are on another root directory (e.g. from an install disk) install syslinux by directing to the chroot:
# syslinux-install_update.sh -i -a -m -c /mnt/

Manual install

  • If you are unsure of which partition table you are using (MBR or GPT), you can check using the following command
# blkid -s PTTYPE -o value /dev/sda
  • 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 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
# cp -r /usr/lib/syslinux/bios/*.c32 /boot/syslinux/                           ## copy ALL the *.c32 files from /usr/lib/syslinux/bios/, DO NOT SYMLINK
# extlinux --install /boot/syslinux

After this, proceed to install the Syslinux boot code (mbr.bin or gptmbr.bin) to Master Boot Record 440-byte boot code region (not to be confused with MBR aka msdos partition table) of the disk, as described in the next section.

MBR partition table

See the main article: Master Boot Record.

Next you need to mark your boot partition active in your partition table. Applications capable of doing this include fdisk, cfdisk, sfdisk, parted/gparted ("boot" flag). 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 if=/usr/lib/syslinux/bios/mbr.bin of=/dev/sda

An alternate 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 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

See the main article: GUID Partition Table.

Bit 2 of the attributes ("legacy_boot" attribute) needs to be set for the /boot partition:.

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

This would toggle the attribute legacy BIOS bootable on partition 1. To check:

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

Install the MBR:

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

If this does not work you can also try:

# syslinux-install_update -i -m

UEFI Systems

  • $esp is the mountpoint of the ESP (EFI System Partition) in the below commands.
  • efi64 denotes x86_64 UEFI systems, for IA32 (32-bit) EFI replace efi64 with efi32 in the below commands.
  • For syslinux, kernel and initramfs files need to be in the 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


  • Copy syslinux files to ESP (replace $esp by the mount point of the ESP, usually /boot):
# mkdir -p $esp/EFI/syslinux
# cp -r /usr/lib/syslinux/efi64/* $esp/EFI/syslinux
# efibootmgr -c -d /dev/sdX -p Y -l /EFI/syslinux/syslinux.efi -L "Syslinux"

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

  • Create or edit $esp/EFI/syslinux/syslinux.cfg by following #Configuration.
Note: The config 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.


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

  • 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.


Note: Any configuration file found in the examples needs to be edited to set the proper kernel parameters. See section #Kernel parameters.

Boot prompt

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


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

Text boot menu

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

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


 UI menu.c32
 LABEL arch
         MENU LABEL Arch Linux
         LINUX ../vmlinuz-linux
         APPEND root=/dev/sda2 rw
         INITRD ../initramfs-linux.img
 LABEL archfallback
         MENU LABEL Arch Linux Fallback
         LINUX ../vmlinuz-linux
         APPEND root=/dev/sda2 rw
         INITRD ../initramfs-linux-fallback.img

For more details about the menu system, see the Syslinux documentation or 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/
Note: If you are using UEFI make sure to copy from /usr/lib/syslinux/efi64/ (efi32 for i686 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 config uses the same menu design as the Arch Install CD, its config can be found at projects.archlinux.org. The Arch Linux background image can be downloaded from there, too. Copy the image to /boot/syslinux/splash.png.


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

Kernel parameters

The kernel parameters are set using the APPEND line in syslinux.cfg. It is recommended to make the following changes for the fallback entry as well.

In the simplest case, the partition name in the root parameter needs to be replaced. Change /dev/sda2 to point to the correct root partition.

APPEND root=/dev/sda2

If you want to use UUID for persistent block device naming change the APPEND line as follows, substituting 1234 with the UUID of your root partition:

APPEND root=UUID=1234 rw

If you use encryption LUKS change the APPEND line to use your encrypted volume:

APPEND root=/dev/mapper/group-name cryptdevice=/dev/sda2:name rw

If you are using software RAID using mdadm, change the APPEND line to accommodate your RAID arrays. As an example the following accommodates three RAID 1 arrays and sets the appropriate one as root:

APPEND root=/dev/md1 rw md=0,/dev/sda2,/dev/sdb2 md=1,/dev/sda3,/dev/sdb3 md=2,/dev/sda4,/dev/sdb4

If booting from a software raid partition fails using the kernel device node method above an alternative, a more reliable, way is to use partition labels:


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.


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


to set a master bootloader password, and


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

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


Note: Syslinux BIOS cannot directly chainload files from other partitions, however chain.c32 can boot partition boot sector (VBR).

If you want to chainload other operating systems (such as Windows) or boot loaders, copy 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.

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).

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

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

For more details about chainloading, see the Syslinux wiki.

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

 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.

 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

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. Essentially, Extlinux can be installed on the partition superblock and be called as a separate bootloader 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 / is on /dev/sda3.

From a booted Linux (likely the partition that Syslinux is set up to boot), mount the other 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 and copy necessary *.c32 files

# extlinux -i /mnt/boot/syslinux
# cp /usr/lib/syslinux/bios/*.c32 /mnt/boot/syslinux

Create /mnt/boot/syslinux/syslinux.cfg. Below is an example:

/boot/syslinux/syslinux.cfg on /dev/sda3
timeout 10

ui menu.c32

label Other Linux
    linux /boot/vmlinuz-linux
    initrd /boot/initramfs-linux.img
    append root=/dev/sda3 rw quiet

label MAIN
    com32 chain.c32
    append hd0 0

taken from Djgera's user wiki page.

Using memtest

Install memtest86+ from the official repositories.

Use this LABEL section to launch memtest:

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

Note: If you are using pxelinux, change 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 (Hardware Detection Tool) displays hardware information. Like before, the .c32 file has to be copied from /boot/syslinux/. For PCI info, copy /usr/share/hwdata/pci.ids to /boot/syslinux/pci.ids and add the following to your configuration file:

 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 this thread .

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
         COM32 poweroff.c32

Clear menu

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


Keyboard layout

If you often have to edit your boot parameters, you might want to remap your keyboard layout. This allows you to enter "=", "/" and other characters easily on a non-US keyboard.

First you have to create a compatible keymap, in this example German:

Note: us.kmap needs to be created or the following will not work.
$ cp /usr/share/kbd/keymaps/i386/qwertz/de.map.gz .
$ cp /usr/share/kbd/keymaps/i386/qwerty/us.map.gz .
$ gunzip de.map.gz
$ gunzip us.map.gz
$ mv de.map de.kmap
$ mv us.map us.kmap
# keytab-lilo de > de.ktl

Copy de.ktl as root to /boot/syslinux/ and set ownership to root:

# chown root:root /boot/syslinux/de.ktl

Now edit syslinux.conf and add:

KBDMAP de.ktl

Hiding the menu

Use the option:


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


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 syslinux.

Copy the {l,}pxelinux.0 bootloader (provided by the syslinux package) 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 "$root/boot"
# cp /usr/lib/syslinux/bios/ldlinux.c32 "$root/boot"
# mkdir "$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.

# vim "$root/boot/pxelinux.cfg/default"
default linux

label linux
kernel vmlinuz-linux
append initrd=initramfs-linux.img quiet ip=:::::eth0:dhcp nfsroot=

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

append ro initrd=initramfs-linux.img ip=:::::eth0:dhcp nbd_host= 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"

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

Merge-arrows-2.pngThis article or section is a candidate for merging with Working with the serial console.Merge-arrows-2.png

Notes: General page about topic not specific to Syslinux, already provides examples for GRUB. (Discuss in Talk:Syslinux#)

To enable Serial Console add the SERIAL port [baudrate] to the top of syslinux.cfg file. "port" is a number (0 for /dev/ttyS0), if "baudrate" is omitted, the baud rate default is 9600 bps. The serial parameters are hardcoded to 8 bits, no parity and 1 stop bit.[1]

SERIAL 0 115200

Enable Serial Console in the kernel at boot by adding console=tty0 console=ttyS0,115200n8 to the APPEND option.[2]

APPEND root=UUID=126ca36d-c853-4f3a-9f46-cdd49d034ce4 rw console=tty0 console=ttyS0,115200n8

How to do this with GRUB: Working_with_the_serial_console#GRUB2_and_systemd


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=/dev/sda2 rw initrd=../initramfs-linux.img

If you do not have access to boot: in ramfs, and therefore temporarily unable to boot 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, use cfdisk to create a FAT16 partition (<=2GB) and format using dosfstools:

# mkfs.msdos -F 16 /dev/sda1

then install and configure Syslinux.

Missing operating system

  • Check that you have installed gptmbr.bin for GPT partition table and mbr.bin for DOS partition table. "Missing operating system" message comes from mbr.bin while gptmbr.bin has message "Missing OS".
  • Check if the partition that contains /boot has the boot flag enabled.
  • Check perhaps first partition at bootable 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 beginners 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=/dev/sda6 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 menu quickly overwrites the text. To avoid losing the log information one needs to disable menu UI 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 one needs to recompile syslinux package with additional CFLAGS:


See also