Syslinux
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.
- 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, [http://bugzilla.syslinux.org/show_bug.cgi?id=33 contact upstream].
- If you are upgrading from Syslinux 4.xx (or 5.xx) to 6.xx version,
please re-install (not update) Syslinux BIOS manually (not using the install script) once by following #Manual install. The install script may not properly upgrade Syslinux to 6.xx version.
Contents
1 BIOS Systems
1.1 Syslinux boot process
- 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 created by extlinux --install command. Note ldlinux.sys is not same as ldlinux.c32.
- 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 64 KB 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 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.
- 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.
1.2 Installation
- Install syslinux package from official repositories.
# pacman -S syslinux
1.2.1 Automatic Install
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.
- 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.
* If you have just cloned your disk to say /mnt/clone, install syslinux by issuing from the Parabola installation medium:
# syslinux-install_update.sh -i -a -m -c /mnt/clone
1.2.2 Manual install
# 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/*.c32 /boot/syslinux/
## copy ALL the *.c32 files from /usr/lib/syslinux/bios/, DO NOT SYMLINK
# 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.
1.2.2.1 MBR partition table
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.
1.2.2.2 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
2 UEFI Systems
- 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.
2.1 Limitations of UEFI Syslinux
- UEFI Syslinux application syslinux.efi cannot be signed by sbsign (from sbsigntool) for UEFI Secure Boot. Bug report - http://bugzilla.syslinux.org/show_bug.cgi?id=8
- Using TAB to edit kernel parameters in UEFI Syslinux menu lead to garbaged display (text on top of one-another). Bug report - http://bugzilla.syslinux.org/show_bug.cgi?id=9
- UEFI Syslinux does not support chainloading other EFI applications like UEFI Shell. Bug report - http://bugzilla.syslinux.org/show_bug.cgi?id=17
- UEFI Syslinux does not boot in Virtual Machines like QEMU/OVMF or VirtualBox or VMware and in some UEFI emulation environments like DUET. Bug reports - http://bugzilla.syslinux.org/show_bug.cgi?id=21 and http://bugzilla.syslinux.org/show_bug.cgi?id=23
- Memdisk is not available for UEFI. Bug report - http://bugzilla.syslinux.org/show_bug.cgi?id=30
2.2 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
- Setup boot entry for Syslinux using efibootmgr:
# 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.
3 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
- TIMEOUT value is in units of 1/10 of a second.
3.1 Examples
3.1.1 Basic configuration
This is a simple configuration file that will show a boot: prompt and automatically boot after 5 seconds.
Configuration:
/boot/syslinux/syslinux.cfg
PROMPT 1
TIMEOUT 50
DEFAULT parabola
LABEL parabola
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre.img
LABEL parabolafallback
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre-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
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 parabola
LABEL parabola
MENU LABEL Parabola GNU/Linux-libre
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre.img
LABEL parabolafallback
MENU LABEL Parabola GNU/Linux-libre Fallback
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre-fallback.img
For more details about the menu system, see the Syslinux documentation.
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/
Configuration:
/boot/syslinux/syslinux.cfg
SERIAL 0 38400
UI boot/syslinux/vesamenu.c32
MENU TITLE Parabola GNU/Linux-libre
MENU BACKGROUND boot/syslinux/splash.png
MENU WIDTH 78
MENU MARGIN 4
MENU ROWS 7
MENU VSHIFT 10
MENU TABMSGROW 14
MENU CMDLINEROW 14
MENU HELPMSGROW 16
MENU HELPMSGENDROW 29
# Refer to http://syslinux.zytor.com/wiki/index.php/Doc/menu
MENU COLOR border 35;40 #ff777caa #a0000000 std
MENU COLOR title 1;35;40 #ff777caa #a0000000 std
MENU COLOR sel 7;35;47 #e0ffffff #20777caa all
MENU COLOR unsel 35;40 #ff777caa #a0000000 std
MENU COLOR help 35;40 #c0b2b2b2 #a0000000 std
MENU COLOR timeout_msg 35;40 #ff777caa #00000000 std
MENU COLOR timeout 1;35;40 #ff777caa #00000000 std
MENU COLOR msg07 35;40 #ff777caa #a0000000 std
MENU COLOR tabmsg 35;40 #ff777caa #00000000 std
LABEL parabola
MENU LABEL Parabola GNU/Linux-libre
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre.img
LABEL parabolafallback
MENU LABEL Parabola GNU/Linux-libre Fallback
LINUX ../vmlinuz-linux-libre
APPEND root=/dev/sda2 rw
INITRD ../initramfs-linux-libre-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.
3.2 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.
3.3 Chainloading
If you want to chainload other operating systems or boot loaders, copy the chain.c32 module to the Syslinux directory (for details, see the instructions in the previous section).
3.4 Chainloading other GNU/Linux systems
If you have another version of GNU/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 Parabola configuration path of /boot/syslinux is being used and the chainloaded / is on /dev/sda3.
From a booted GNU/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 GNU/Linux
linux /boot/vmlinuz-linux-libre
initrd /boot/initramfs-linux-libre.img
append root=/dev/sda3 rw quiet
label MAIN
com32 chain.c32
append hd0 0
3.5 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
...
3.6 HDT
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:
/boot/syslinux/syslinux.cfg
LABEL hdt
MENU LABEL Hardware Info
COM32 hdt.c32
3.7 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
To clear the screen when exiting the menu, add the following line:
/boot/syslinux/syslinux.cfg
MENU CLEAR
3.9 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
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.
3.11 Pxelinux
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 "$root/boot/pxelinux.cfg"
We also created the pxelinux.cfg directory, which is where pxelinux searches for configuration files by default. Because we do not want to discriminate between different host MACs, we then create the default configuration.
# vim "$root/boot/pxelinux.cfg/default"
default gnulinux label gnulinux kernel vmlinuz-linux-libre append initrd=initramfs-linux-libre.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-libre.img ip=:::::eth0:dhcp nbd_host=10.0.0.1 nbd_name=arch root=/dev/nbd0
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"
4 Troubleshooting
4.1 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: parabola
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-libre root=/dev/sda2 rw initrd=../initramfs-linux-libre.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.
4.2 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.
4.3 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.
4.4 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 Parabola 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.
4.5 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. parabola).
4.6 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
Problem: As of linux-libre-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
