Syslinux

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Summary
Describes installing and configuring Syslinux, a collection of bootloaders.
Overview
In order to boot Arch Linux, a Linux-capable boot loader such as GRUB(2), Syslinux, LILO or GRUB Legacy must be installed to the Master Boot Record or the GUID Partition Table. The boot loader is responsible for loading the kernel and initial ramdisk before initiating the boot process.

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 (as of version 6.02, in both BIOS and UEFI) cannot access files from partitions other than its own (unlike GRUB). This feature (called multi-fs) is yet to be implemented upstream. If you want to help with the multi-fs feature, contact upstream.

Contents

BIOS Systems

Syslinux boot process

  1. Load MBR. At boot, the computer loads the MBR (/usr/lib/syslinux/bios/mbr.bin).
  2. Search active partition. The MBR looks for the partition that is marked as active (boot flag).
  3. Execute volume boot record. Once found, the volume boot record (VBR) will be executed. In the case of ext2/3/4 and FAT12/16/32, the starting sector of ldlinux.sys is hard-coded into the VBR.
  4. Execute ldlinux.sys. The VBR will execute (ldlinux.sys). Therefore, if the location of ldlinux.sys changes, Syslinux will no longer boot. (In the case of Btrfs, the above method will not work since files move around resulting in the sector location of ldlinux.sys changing. Therefore, the entire Syslinux code needs to be stored outside the filesystem. The code is stored in the sectors following the VBR.)
  5. Search configuration file. Once Syslinux is fully loaded, it looks for a configuration file, either extlinux.conf or syslinux.cfg.
  6. Load configuration. If one is found, the configuration file is loaded. If no configuration file is found, you will be given a Syslinux prompt.

Installation 

# pacman -S syslinux
Note:
  • 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

The syslinux-install_update script will install Syslinux, copy/symlink *.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.

1. 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.
2. 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
3. Create or Edit /boot/syslinux/syslinux.cfg by following #Configuration.
Note:
  • 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 have just cloned your disk to say /mnt/clone, install syslinux by issuing from the Arch installation medium: 
# syslinux-install_update.sh -i -a -m -c /mnt/clone

Manual install

Note:
  • 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
gpt
  • 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/* /boot/syslinux
# extlinux --install /boot/syslinux

After this 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.

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 conv=notrunc 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 conv=notrunc of=/dev/sda

In this case, a single byte of value 5 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

Note:
  • UEFI support is available only from Syslinux 6.xx onwards.
  • $esp is the mountpoint of the ESP 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

Installation

  • Install syslinux package and setup syslinux in the EFI System Partition (ESP) as follows: 
# pacman -S syslinux
  • Copy syslinux files to ESP 
# mkdir -p $esp/EFI/syslinux
# cp -r /usr/lib/syslinux/efi64/* $esp/EFI/syslinux

# mount -t efivarfs efivarfs /sys/firmware/efi/efivars
# efibootmgr -c -d /dev/sdX -p Y -l /EFI/syslinux/syslinux.efi -L "Syslinux"
  • 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.

Configuration

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

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

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 1/10 of a second.

Examples

Basic configuration

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

Note: The partition in question needs to be whatever you have as / (root), not /boot.

Configuration: 

/boot/syslinux/syslinux.cfg
 PROMPT 1
 TIMEOUT 50
 DEFAULT arch
 
 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

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

If you want to use UUID for persistent device naming instead of device names, change the APPEND line to your equivalent UUID of the root partition: 

APPEND root=UUID=978e3e81-8048-4ae1-8a06-aa727458e8ff 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 array's 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: 

APPEND root=LABEL=THEROOTPARTITIONLABEL rw

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/

Configuration: 

/boot/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=/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.

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/

This config uses the same menu design as the Arch Install CD. The background file can be found there too. To make sure that your system can boot with this config, check that it is pointing to the correct partition.

Configuration: 

/boot/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 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.

Auto boot

If you do not want to see the Syslinux menu at all, comment out all UI commands and make sure there is a DEFAULT set in your syslinux.cfg.

Chainloading

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 (or symlink) the chain.c32 module to the Syslinux directory (for details, see the instructions in the previous section). Then create a section in the configuration file: 

/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.

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.

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
...

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/{chain,menu}.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: 

/boot/syslinux/syslinux.cfg
...
 LABEL memtest
         MENU LABEL Memtest86+
         LINUX ../memtest86+/memtest.bin
...

HDT

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

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
         COMBOOT poweroff.com

Clear menu

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

/boot/syslinux/syslinux.cfg
 MENU CLEAR

Keyboard remapping

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 (for example a German one): 

# cp /usr/share/kbd/keymaps/i386/qwerty/us.map.gz ./
# cp /usr/share/kbd/keymaps/i386/qwertz/de.map.gz ./
# gunzip {de,us}.map.gz
# mv de.{,k}map
# mv us.{,k}map
# keytab-lilo de > de.ktl

The last command has to be run as root, otherwise it will not work.

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: 

/boot/syslinux/syslinux.cfg
 KBDMAP de.ktl

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: Syslinux at present has no UEFI networking stack, so you'll be unable to use syslinux-efi-git (as is possible with #GRUB) and still expect to be able to tftp your kernel and initramfs; pxelinux still works fine for legacy PXE booting

Pxelinux is provided by syslinux.

Copy the pxelinux bootloader (provided by the syslinux package) to the boot directory of the client. 

# cp /usr/lib/syslinux/bios/pxelinux.0 "$root/boot"
# mkdir "$root/boot/pxelinux.cfg"

We also created the pxelinux.cfg directory, which is where pxelinux searches for configuration files by default. Because we don't 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=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_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)

The pxelinux configuration syntax identical to 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"

Troubleshooting

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

If you get this message, check if the partition that contains /boot has the boot flag enabled. If the flag is enabled, then perhaps this partition 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 doesn't understand. As of August 2013 by default mdadm will create an array with version 1.2 metadata, but Syslinux doesn't understand metadata newer than 1.0. If this is the case you'll 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).

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 doesn't 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.

See also

Retrieved from "https://wiki.archlinux.org/index.php?title=Syslinux&oldid=280349"