Difference between revisions of "Diskless system"

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[[Category:Getting and installing Arch]]
 
[[Category:Getting and installing Arch]]
{{Article summary start}}
+
[[ja:ディスクレスシステム]]
{{Article summary text|Detailed explanation of diskless system setup.}}
+
[[zh-cn:Diskless system]]
{{Article summary heading|Related}}
+
{{Related articles start}}
{{Article summary wiki|NFS}}
+
{{Related|NFS}}
{{Article summary wiki|NFS Troubleshooting}}
+
{{Related|NFS Troubleshooting}}
{{Article summary wiki|PXE}}
+
{{Related|PXE}}
{{Article summary wiki|Mkinitcpio#Using_net}}
+
{{Related|Mkinitcpio#Using_net}}
{{Article summary end}}
+
{{Related articles end}}
 +
 
 
From [[Wikipedia:Diskless node]]
 
From [[Wikipedia:Diskless node]]
 
:''A diskless node (or diskless workstation) is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server.''
 
:''A diskless node (or diskless workstation) is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server.''
  
==Server configuration==
+
== Server configuration ==
  
 
First of all, we must install the following components:
 
First of all, we must install the following components:
 
* A [[Dhcpd|DHCP]] server to assign IP addresses to our diskless nodes.
 
* A [[Dhcpd|DHCP]] server to assign IP addresses to our diskless nodes.
* A [[Tftpd_server|TFTP]] server to transfer the boot image (a requirement of all PXE option roms).  
+
* A [[TFTP]] server to transfer the boot image (a requirement of all PXE option roms).
 
* A form of network storage ([[NFS]] or NBD) to export the Arch installation to the diskless node.
 
* A form of network storage ([[NFS]] or NBD) to export the Arch installation to the diskless node.
  
 
{{Note|{{pkg|dnsmasq}} is capable of simultaneously acting as both DHCP and TFTP server. For more information, see the [[dnsmasq]] article.}}
 
{{Note|{{pkg|dnsmasq}} is capable of simultaneously acting as both DHCP and TFTP server. For more information, see the [[dnsmasq]] article.}}
  
===DHCP===
+
=== DHCP ===
 
+
Install ISC {{pkg|dhcp}}.
+
 
+
{{bc|# pacman -Syu dhcp}}
+
  
Configure ISC DHCP.
+
Install ISC {{Pkg|dhcp}} and configure it:
  
{{hc|# vim /etc/dhcpd.conf|2=
+
{{hc|/etc/dhcpd.conf|2=
<nowiki>allow booting;
+
allow booting;
 
allow bootp;
 
allow bootp;
  
Line 35: Line 32:
  
 
option domain-name-servers 10.0.0.1;
 
option domain-name-servers 10.0.0.1;
 +
 +
option architecture code 93 = unsigned integer 16;
  
 
group {
 
group {
 
     next-server 10.0.0.1;
 
     next-server 10.0.0.1;
     filename "pxelinux.0";
+
 
 +
     if option architecture = 00:07 {
 +
        filename "/grub/x86_64-efi/core.efi";
 +
    } else {
 +
        filename "/grub/i386-pc/core.0";
 +
    }
  
 
     subnet 10.0.0.0 netmask 255.255.255.0 {
 
     subnet 10.0.0.0 netmask 255.255.255.0 {
Line 44: Line 48:
 
         range 10.0.0.128 10.0.0.254;
 
         range 10.0.0.128 10.0.0.254;
 
     }
 
     }
}</nowiki>}}
+
}
 +
}}
  
 
{{Note|{{ic|next-server}} should be the address of the TFTP server; everything else should be changed to match your network}}
 
{{Note|{{ic|next-server}} should be the address of the TFTP server; everything else should be changed to match your network}}
  
Start ISC DHCP.
+
RFC 4578 defines the "Client System Architecture Type" dhcp option. In the above configuration, if the PXE client requests an x86_64-efi binary (type 0x7), we appropriately give them one, otherwise falling back to the legacy binary. This allows both UEFI and legacy BIOS clients to boot simultaneously on the same network segment.
  
{{bc|# systemctl start dhcpd4.service}}
+
Start ISC DHCP [[systemd]] service.
  
===TFTP===
+
=== TFTP ===
  
The TFTP server will be used to transfer the kernel, initramfs, and pxelinux to the client.
+
The TFTP server will be used to transfer the bootloader, kernel, and initramfs to the client.
  
See [[Tftpd server]] for tftpd installation and configuration. You need to set  ftpd server root to:
+
Set the TFTP root to {{ic|/srv/arch/boot}}. See [[Tftpd server]] for installation and configuration.
* {{ic|/srv/arch/boot}} if you are not going to use NBD.
+
* {{ic|/srv/boot}}  if you're going to use NBD, because you'll be unable to mount your root filesystem while in use.
+
  
===Network storage===
+
=== Network storage ===
  
The primary difference between using NFS and NBD is while with both you can in fact have multiple clients using the same installation, with NBD (by the nature of manipulating a filesystem directly) you'll need to use the {{ic|copyonwrite}} mode to do so, which ends up discarding all writes on client disconnect. In some situations however, this might be highly desirable.
+
The primary difference between using NFS and NBD is while with both you can in fact have multiple clients using the same installation, with NBD (by the nature of manipulating a filesystem directly) you will need to use the {{ic|copyonwrite}} mode to do so, which ends up discarding all writes on client disconnect. In some situations however, this might be highly desirable.
  
====NFS====
+
==== NFS ====
  
Install {{pkg|nfs-utils}} on the server.
+
Install {{Pkg|nfs-utils}} on the server.
  
{{bc|# pacman -Syu nfs-utils}}
+
You will need to add the root of your Arch installation to your [[NFS]] exports:
  
=====[[NFS|NFSv4]]=====
+
{{hc|/etc/exports|2=
 
+
/srv       *(rw,fsid=0,no_root_squash,no_subtree_check)
You'll need to add the root of your arch installation to your NFS exports:
+
/srv/arch  *(rw,no_root_squash,no_subtree_check)
 
+
{{hc|# vim /etc/exports|2=
+
/srv/arch *(rw,fsid=0,no_root_squash,no_subtree_check)
+
 
}}
 
}}
  
Next, start NFS.
+
Next, start NFS services: {{ic|rpc-idmapd}} {{ic|rpc-mountd}}.
  
{{bc|# systemctl start rpc-idmapd.service rpc-mountd.service}}
+
==== NBD ====
  
=====[[NFSv3]]=====
+
Install {{Pkg|nbd}} and configure it.
 
+
{{hc|# vim /etc/exports|2=
+
/srv/arch *(rw,no_root_squash,no_subtree_check,sync)
+
}}
+
 
+
Next, start NFSv3.
+
 
+
{{bc|# systemctl start rpc-mountd.service rpc-statd.service}}
+
 
+
{{Note|If you're not worried about data loss in the event of network and/or server failure, replace {{ic|sync}} with {{ic|async}}--additional options can be found in the [[NFS]] article.}}
+
 
+
====NBD====
+
 
+
Install {{pkg|nbd}}.
+
 
+
{{bc|# pacman -Syu nbd}}
+
 
+
Configure nbd.
+
  
 
{{hc|# vim /etc/nbd-server/config|2=
 
{{hc|# vim /etc/nbd-server/config|2=
Line 108: Line 90:
 
[arch]
 
[arch]
 
     exportname = /srv/arch.img
 
     exportname = /srv/arch.img
     copyonwrite = false}}
+
     copyonwrite = false
 +
}}
  
{{note|Set {{ic|copyonwrite}} to true if you want to have multiple clients using the same NBD share simultaneously; refer to {{ic|man 5 nbd-server}} for more details.}}
+
{{Note|Set {{ic|copyonwrite}} to true if you want to have multiple clients using the same NBD share simultaneously; refer to {{ic|man 5 nbd-server}} for more details.}}
  
Start nbd.
+
Start {{ic|nbd}} systemd service.
  
{{bc|# systemctl start nbd.service}}
+
== Client installation ==
 
+
==Client installation==
+
  
 
Next we will create a full Arch Linux installation in a subdirectory on the server. During boot, the diskless client will get an IP address from the DHCP server, then boot from the host using PXE and mount this installation as its root.
 
Next we will create a full Arch Linux installation in a subdirectory on the server. During boot, the diskless client will get an IP address from the DHCP server, then boot from the host using PXE and mount this installation as its root.
  
===Directory setup===
+
=== Directory setup ===
  
Create a [[Wikipedia: Sparse file|sparse file]] of at least 1 gigabyte, and create an ext4 filesystem on it (you can of course also use a real block device or [[LVM]] if you so desire).
+
Create a [[Wikipedia: Sparse file|sparse file]] of at least 1 gigabyte, and create a btrfs filesystem on it (you can of course also use a real block device or [[LVM]] if you so desire).
  
{{bc|1=
+
# truncate -s 1G /srv/arch.img
# truncate -s 1G /srv/arch.img
+
# mkfs.btrfs /srv/arch.img
# mkfs.btrfs /srv/arch.img
+
# export root=/srv/arch
# export root=/srv/arch
+
# mkdir -p "$root"
# mkdir -p "$root"
+
# mount -o loop,discard,compress=lzo /srv/arch.img "$root"
# mount -o loop,discard,compress=lzo /srv/arch.img "$root"}}
+
  
 
{{Note|Creating a separate filesystem is required for NBD but optional for NFS and can be skipped/ignored.}}
 
{{Note|Creating a separate filesystem is required for NBD but optional for NFS and can be skipped/ignored.}}
  
===Bootstrapping installation===
+
=== Bootstrapping installation ===
 
+
Install {{pkg|devtools}} and {{pkg|arch-install-scripts}}, and run {{ic|mkarchroot}}.
+
 
+
{{bc|1=
+
# pacman -Syu devtools arch-install-scripts
+
# mkarchroot -f "$root" base '''mkinitcpio-nfs-utils''' '''nfs-utils'''}}
+
 
+
{{Note|In all cases {{pkg|mkinitcpio-nfs-utils}} is still required--{{ic|ipconfig}} used in early-boot is provided only by the latter.}}
+
  
Now the initramfs needs to be constructed. The shortest configuration, [[#NFSv3]], is presented as a "base" upon which all subsequent sections modify as-needed.
+
{{Accuracy|{{ic|mkarchroot}} is mentioned only in the following sentence.}}
  
====[[NFSv3]]====
+
Install {{Pkg|devtools}} and {{Pkg|arch-install-scripts}}, and run {{ic|mkarchroot}}.
  
{{hc|# vim "$root/etc/mkinitcpio.conf"|2=
+
# pacstrap -d "$root" base mkinitcpio-nfs-utils nfs-utils
MODULES="nfsv3"
+
HOOKS="base udev autodetect '''net''' filesystems"
+
BINARIES=""}}
+
  
The initramfs now needs to be rebuilt; the easiest way to do this is via {{ic|[[Change Root|arch-chroot]]}}.
+
{{Note|In all cases {{Pkg|mkinitcpio-nfs-utils}} is still required. {{ic|ipconfig}} used in early-boot is provided only by the latter.}}
  
{{bc|1=
+
Now the initramfs needs to be constructed.
# arch-chroot "$root" /bin/bash
+
(chroot) # mkinitcpio -p linux
+
(chroot) # exit}}
+
  
====[[NFS|NFSv4]]====
+
==== NFS ====
  
 
Trivial modifications to the {{ic|net}} hook are required in order for NFSv4 mounting to work (not supported by {{ic|nfsmount}}--the default for the {{ic|net}} hook).
 
Trivial modifications to the {{ic|net}} hook are required in order for NFSv4 mounting to work (not supported by {{ic|nfsmount}}--the default for the {{ic|net}} hook).
  
{{bc|1=<nowiki>
+
# sed s/nfsmount/mount.nfs4/ "$root/usr/lib/initcpio/hooks/net" > "$root/usr/lib/initcpio/hooks/net_nfs4"
# sed s/nfsmount/mount.nfs4/ "$root/usr/lib/initcpio/hooks/net" | tee "$root/usr/lib/initcpio/hooks/net_nfs4"
+
# cp $root/usr/lib/initcpio/install/net{,_nfs4}
# cp "$root/usr/lib/initcpio/install/{net,net_nfs4}"</nowiki>}}
+
  
 
The copy of {{ic|net}} is unfortunately needed so it does not get overwritten when {{pkg|mkinitcpio-nfs-utils}} is updated on the client installation.
 
The copy of {{ic|net}} is unfortunately needed so it does not get overwritten when {{pkg|mkinitcpio-nfs-utils}} is updated on the client installation.
  
From the base {{ic|mkinitcpio.conf}}, replace the {{ic|nfsv3}} module with {{ic|nfsv4}}, replace {{ic|net}} with {{ic|net_nfs4}}, and add {{ic|/sbin/mount.nfs4}} to {{ic|BINARIES}}.
+
Edit {{ic|$root/etc/mkinitcpio.conf}} and add {{ic|nfsv4}} to {{ic|MODULES}}, {{ic|net_nfs4}} to {{ic|HOOKS}}, and {{ic|/usr/bin/mount.nfs4}} to {{ic|BINARIES}}.
  
====NBD====
+
Next, we [[chroot]] our installation and run ''mkinitcpio'':
  
The {{aur|mkinitcpio-ndb}} package needs to be installed on the client.
+
# arch-chroot "$root" mkinitcpio -p linux
  
{{bc|1=<nowiki>
+
==== NBD ====
# pacman --root "$root" --dbpath "$root/var/lib/pacman" -U mkinitcpio-nbd-0.4-1-any.pkg.tar</nowiki>}}
+
  
You will then need to append {{ic|nbd}} to your {{ic|HOOKS}} array after {{ic|net}}.
+
The {{AUR|mkinitcpio-nbd}} package needs to be installed on the client. Build it with ''makepkg'' and install it:
  
==Client configuration==
+
# pacman --root "$root" --dbpath "$root/var/lib/pacman" -U mkinitcpio-nbd-0.4-1-any.pkg.tar.xz
  
Be sure your NIC driver is built into the kernel for your client installation and not loaded as a module. Otherwise ipconfig won't be able to find your network adapter on boot and your NFS or NBD mount will fail. Be aware this may require compiling a [[Kernels#Compilation| custom kernel]].
+
You will then need to append {{ic|nbd}} to your {{ic|HOOKS}} array after {{ic|net}}; {{ic|net}} will configure your networking for you, but not attempt a NFS mount if {{ic|nfsroot}} is not specified in the kernel line.
In addition to the setup mentioned here, you should also set up your [[HOSTNAME#Set_the_host_name|hostname]], [[Timezone#Time_Zone|timezone]], [[Locale#Setting_system-wide_locale|locale]], and [[KEYMAP|keymap]], and follow any other relevant parts of the [[Installation Guide]].
+
  
===Bootloader===
+
== Client configuration ==
  
====[[Syslinux|Pxelinux]]====
+
In addition to the setup mentioned here, you should also set up your [[HOSTNAME#Set_the_host_name|hostname]], [[Timezone#Time_Zone|timezone]], [[Locale#Setting the system locale|locale]], and [[keymap]], and follow any other relevant parts of the [[Installation guide]].
  
{{Merge|Syslinux|}}
+
=== Bootloader ===
  
Install {{pkg|syslinux}}.
+
==== GRUB ====
  
{{bc|1=
+
{{Merge|GRUB|}}
# pacman -Syu syslinux}}
+
  
Copy the pxelinux bootloader (provided by the syslinux package) to the boot directory of the client.
+
Though poorly documented, GRUB supports being loaded via PXE.
  
{{bc|1=
+
# pacman --root "$root" --dbpath "$root/var/lib/pacman" -S grub
# cp /usr/lib/syslinux/pxelinux.0 "$root/boot"
+
# mkdir "$root/boot/pxelinux.cfg"}}
+
  
We also created the {{ic|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 {{ic|default}} configuration.
+
Create a grub prefix on the target installation for both architectures using {{ic|grub-mknetdir}}.
  
{{hc|# vim "$root/boot/pxelinux.cfg/default"|<nowiki>
+
# arch-chroot "$root" grub-mknetdir --net-directory=/boot --subdir=grub
default linux
+
  
label linux
+
Luckily for us, grub-mknetdir creates prefixes for all currently compiled/installed targets, and the {{Pkg|grub}} maintainers were nice enough to give us both in the same package, thus grub-mknetdir only needs to be run once.
kernel vmlinuz-linux
+
append initrd=initramfs-linux.img ip=:::::eth0:dhcp nfsroot=10.0.0.1:/
+
</nowiki>}}
+
  
[[NFSv3]] mountpoints are relative to the root of the server, not {{ic|<nowiki>fsid=0</nowiki>}}. If you're using NFSv3, you'll need to pass {{ic|10.0.0.1:/srv/arch}} to {{ic|nfsroot}}.
+
Now we create a trivial GRUB configuration:
  
Or if you are using NBD, use the following append line:
+
{{hc|# vim "$root/boot/grub/grub.cfg"|2=
 +
menuentry "Arch Linux" {
 +
    linux /vmlinuz-linux quiet add_efi_memmap ip=:::::eth0:dhcp nfsroot=10.0.0.1:/arch
 +
    initrd /initramfs-linux.img
 +
}
 +
}}
  
{{bc|<nowiki>append initrd=initramfs-linux.img ip=:::::eth0:dhcp nbd_host=10.0.0.1 nbd_name=arch root=/dev/nbd0</nowiki>}}
+
[[GRUB]] dark-magic will {{ic|1=set root=(tftp,10.0.0.1)}} automatically, so that the kernel and initramfs are transferred via TFTP without any additional configuration, though you might want to set it explicitly if you have any other non-tftp menuentries.
  
{{Note|You will need to change {{ic|nbd_host}} and/or {{ic|nfsroot}}, respectively, to match your network configuration (the address of the NFS/NBD server)}}
+
{{Note|Modify your kernel line as-necessary, refer to [[Syslinux#Pxelinux|Pxelinux]] for NBD-related options}}
  
The pxelinux configuration syntax identical to syslinux; refer to the upstream documentation for more information.
+
==== Pxelinux====
  
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.
+
[[Syslinux|Pxelinux]] is provided by {{Pkg|syslinux}}, see [[Syslinux#Pxelinux|here]] for detail.
  
====[[GRUB]]====
+
=== Additional mountpoints ===
  
{{Merge|GRUB2|}}
+
==== NBD root ====
  
Though poorly documented, grub also supports being loaded via PXE. Because of an [https://savannah.gnu.org/bugs/?36755 endianness bug] in {{ic|grub-core/net/tftp.c}} not fixed until bzr revision [http://bzr.savannah.gnu.org/lh/grub/trunk/grub/revision/4548 4548] ({{pkg|grub-bios}} 2.00 is revision [http://bzr.savannah.gnu.org/lh/grub/trunk/grub/revision/4542 4542]), you will need to install {{aur|grub-bios-bzr}}; it makes the most sense to do this on the host installation. The [[Arch User Repository]] article describes how to build AUR packages.
+
In late boot, you will want to switch your root filesystem mount to both {{ic|rw}}, and enable {{ic|1=compress=lzo}}, for much improved disk performance in comparison to [[NFS]].
  
{{Note|If you build {{aur|grub-bios-bzr}} on the host installation and your target architecture doesn't match; you'll end up needing to build it on the target installation instead}}
+
{{hc|# vim "$root/etc/fstab"|2=
 +
/dev/nbd0  /  btrfs  rw,noatime,discard,compress=lzo  0 0
 +
}}
  
{{bc|# pacman --root "$root" --dbpath "$root/var/lib/pacman" -U grub-bios-bzr-4599-1-x86_64.pkg.tar.xz}}
+
==== Program state directories ====
  
Only because we want to use the {{aur|grub-bios-bzr}} installation on the target, we {{ic|arch-chroot}} the target installation so we can use its {{ic|grub-mknetdir}} instead.
+
{{Accuracy|systemd does not use persistent logging by default when /var/log/journal is in tmpfs and/or does not exist}}
  
{{bc|1=
+
You could mount {{ic|/var/log}}, for example, as tmpfs so that logs from multiple hosts do not mix unpredictably, and do the same with {{ic|/var/spool/cups}}, so the 20 instances of cups using the same spool do not fight with each other and make 1,498 print jobs and eat an entire ream of paper (or worse: toner cartridge) overnight.
# arch-chroot /srv/arch
+
(chroot) # grub-mknetdir --net-directory=/boot/ --subdir=/grub
+
(chroot) # exit}}
+
 
+
{{Note|You will need to change the {{ic|filename}} directive in {{ic|/etc/dhcpd.conf}} to {{ic|/grub/i386-pc/core.0}} as {{ic|grub-mknetdir}} will tell you}}
+
 
+
Now we create a trivial QnD grub configuration
+
 
+
{{hc|# vim "$root/boot/grub/grub.cfg"|2=<nowiki>
+
menuentry "Arch Linux" {
+
    linux /vmlinuz-linux ip=:::::eth0:dhcp nfsroot=10.0.0.1:/
+
    initrd /initramfs-linux.img
+
}</nowiki>}}
+
 
+
[[GRUB]] dark-magic will {{ic|<nowiki>set root=(pxe:10.0.0.1)</nowiki>}} automatically, so that the kernel and initramfs are transferred via TFTP without any additional configuration.
+
 
+
{{Note|Modify your kernel line as-necessary, refer to [[#Pxelinux]] for NBD-related options}}
+
 
+
===Additional mountpoints===
+
 
+
You could mount {{ic|/var/log}}, for example, as tmpfs so that logs from multiple hosts don't mix unpredictably, and do the same with {{ic|/var/spool/cups}}, so the 20 instances of cups using the same spool don't fight with each other and make 1,498 print jobs and eat an entire ream of paper (or worse: toner cartridge) overnight.
+
  
 
{{hc|# vim "$root/etc/fstab"|2=
 
{{hc|# vim "$root/etc/fstab"|2=
 
tmpfs  /var/log        tmpfs    nodev,nosuid    0 0
 
tmpfs  /var/log        tmpfs    nodev,nosuid    0 0
tmpfs  /var/spool/cups cups      nodev,nosuid    0 0}}
+
tmpfs  /var/spool/cups tmpfs    nodev,nosuid    0 0}}
  
 
It would be best to configure software that has some sort of state/database to use unique state/database storage directories for each host. If you wanted to run [http://puppetlabs.com/ puppet], for example, you could simply use the {{ic|%H}} specifier in the puppet unit file:
 
It would be best to configure software that has some sort of state/database to use unique state/database storage directories for each host. If you wanted to run [http://puppetlabs.com/ puppet], for example, you could simply use the {{ic|%H}} specifier in the puppet unit file:
  
{{hc|# vim "$root/etc/systemd/system/puppetagent.service"|2=<nowiki>
+
{{hc|# vim "$root/etc/systemd/system/puppetagent.service"|2=
 
[Unit]
 
[Unit]
 
Description=Puppet agent
 
Description=Puppet agent
Line 278: Line 220:
  
 
[Install]
 
[Install]
WantedBy=multi-user.target</nowiki>}}
+
WantedBy=multi-user.target
 +
}}
  
 
Puppet-agent creates vardir and ssldir if they do not exist.
 
Puppet-agent creates vardir and ssldir if they do not exist.
Line 284: Line 227:
 
If neither of these approaches are appropriate, the last sane option would be to create a [http://www.freedesktop.org/wiki/Software/systemd/Generators systemd generator] that creates a mount unit specific to the current host (specifiers are not allowed in mount units, unfortunately).
 
If neither of these approaches are appropriate, the last sane option would be to create a [http://www.freedesktop.org/wiki/Software/systemd/Generators systemd generator] that creates a mount unit specific to the current host (specifiers are not allowed in mount units, unfortunately).
  
==Client boot==
+
== Client boot ==
  
===NBD===
+
=== NBD ===
  
 
{{Accuracy|When using COW on the server, the clients all effectively have read-only mounts of the original filesystem; it should theoretically be safe to do a read-write mount on the NBD server}}
 
{{Accuracy|When using COW on the server, the clients all effectively have read-only mounts of the original filesystem; it should theoretically be safe to do a read-write mount on the NBD server}}
  
If you're using NBD, you'll need to umount the {{ic|arch.img}} before/while you boot your client.
+
If you are using NBD, you will need to umount the {{ic|arch.img}} before/while you boot your client.
  
This makes things particularly interesting when it comes to kernel updates. You can't have your client filesystem mounted while you're booting a client, but that also means you need to use a kernel separate from your client filesystem in order to build it.
+
This makes things particularly interesting when it comes to kernel updates. You cannot have your client filesystem mounted while you are booting a client, but that also means you need to use a kernel separate from your client filesystem in order to build it.
  
You'll need to first copy $root/boot from the client installation to your tftp root (i.e. /srv/boot).
+
You will need to first copy {{ic|$root/boot}} from the client installation to your tftp root (i.e. {{ic|/srv/boot}}).
  
{{bc|# cp -r "$root/boot" /srv/boot}}
+
# cp -r "$root/boot" /srv/boot
  
You'll then need to umount $root before you start the client.
+
You will then need to umount {{ic|$root}} before you start the client.
  
{{bc|# umount "$root"}}
+
# umount "$root"
  
 
{{Note|To update the kernel in this setup, you either need to mount {{ic|/srv/boot}} using [[NFS]] in [[fstab]] on the client (prior to doing the kernel update) or mount your client filesystem after the client has disconnected from NBD}}
 
{{Note|To update the kernel in this setup, you either need to mount {{ic|/srv/boot}} using [[NFS]] in [[fstab]] on the client (prior to doing the kernel update) or mount your client filesystem after the client has disconnected from NBD}}
  
==References==
+
== See also ==
 
+
[https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt kernel.org: Mounting the root filesystem via NFS (nfsroot)]
+
  
[http://www.syslinux.org/wiki/index.php/PXELINUX syslinux.org: pxelinux FAQ]
+
* [https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt kernel.org: Mounting the root filesystem via NFS (nfsroot)]
 +
* [http://www.syslinux.org/wiki/index.php/PXELINUX syslinux.org: pxelinux FAQ]

Latest revision as of 21:19, 16 July 2016

From Wikipedia:Diskless node

A diskless node (or diskless workstation) is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server.

Server configuration

First of all, we must install the following components:

  • A DHCP server to assign IP addresses to our diskless nodes.
  • A TFTP server to transfer the boot image (a requirement of all PXE option roms).
  • A form of network storage (NFS or NBD) to export the Arch installation to the diskless node.
Note: dnsmasq is capable of simultaneously acting as both DHCP and TFTP server. For more information, see the dnsmasq article.

DHCP

Install ISC dhcp and configure it:

/etc/dhcpd.conf
allow booting;
allow bootp;

authoritative;

option domain-name-servers 10.0.0.1;

option architecture code 93 = unsigned integer 16;

group {
    next-server 10.0.0.1;

    if option architecture = 00:07 {
        filename "/grub/x86_64-efi/core.efi";
    } else {
        filename "/grub/i386-pc/core.0";
    }

    subnet 10.0.0.0 netmask 255.255.255.0 {
        option routers 10.0.0.1;
        range 10.0.0.128 10.0.0.254;
    }
}
Note: next-server should be the address of the TFTP server; everything else should be changed to match your network

RFC 4578 defines the "Client System Architecture Type" dhcp option. In the above configuration, if the PXE client requests an x86_64-efi binary (type 0x7), we appropriately give them one, otherwise falling back to the legacy binary. This allows both UEFI and legacy BIOS clients to boot simultaneously on the same network segment.

Start ISC DHCP systemd service.

TFTP

The TFTP server will be used to transfer the bootloader, kernel, and initramfs to the client.

Set the TFTP root to /srv/arch/boot. See Tftpd server for installation and configuration.

Network storage

The primary difference between using NFS and NBD is while with both you can in fact have multiple clients using the same installation, with NBD (by the nature of manipulating a filesystem directly) you will need to use the copyonwrite mode to do so, which ends up discarding all writes on client disconnect. In some situations however, this might be highly desirable.

NFS

Install nfs-utils on the server.

You will need to add the root of your Arch installation to your NFS exports:

/etc/exports
/srv       *(rw,fsid=0,no_root_squash,no_subtree_check)
/srv/arch  *(rw,no_root_squash,no_subtree_check)

Next, start NFS services: rpc-idmapd rpc-mountd.

NBD

Install nbd and configure it.

# vim /etc/nbd-server/config
[generic]
    user = nbd
    group = nbd
[arch]
    exportname = /srv/arch.img
    copyonwrite = false
Note: Set copyonwrite to true if you want to have multiple clients using the same NBD share simultaneously; refer to man 5 nbd-server for more details.

Start nbd systemd service.

Client installation

Next we will create a full Arch Linux installation in a subdirectory on the server. During boot, the diskless client will get an IP address from the DHCP server, then boot from the host using PXE and mount this installation as its root.

Directory setup

Create a sparse file of at least 1 gigabyte, and create a btrfs filesystem on it (you can of course also use a real block device or LVM if you so desire).

# truncate -s 1G /srv/arch.img
# mkfs.btrfs /srv/arch.img
# export root=/srv/arch
# mkdir -p "$root"
# mount -o loop,discard,compress=lzo /srv/arch.img "$root"
Note: Creating a separate filesystem is required for NBD but optional for NFS and can be skipped/ignored.

Bootstrapping installation

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: mkarchroot is mentioned only in the following sentence. (Discuss in Talk:Diskless system#)

Install devtools and arch-install-scripts, and run mkarchroot.

# pacstrap -d "$root" base mkinitcpio-nfs-utils nfs-utils
Note: In all cases mkinitcpio-nfs-utils is still required. ipconfig used in early-boot is provided only by the latter.

Now the initramfs needs to be constructed.

NFS

Trivial modifications to the net hook are required in order for NFSv4 mounting to work (not supported by nfsmount--the default for the net hook).

# sed s/nfsmount/mount.nfs4/ "$root/usr/lib/initcpio/hooks/net" > "$root/usr/lib/initcpio/hooks/net_nfs4"
# cp $root/usr/lib/initcpio/install/net{,_nfs4}

The copy of net is unfortunately needed so it does not get overwritten when mkinitcpio-nfs-utils is updated on the client installation.

Edit $root/etc/mkinitcpio.conf and add nfsv4 to MODULES, net_nfs4 to HOOKS, and /usr/bin/mount.nfs4 to BINARIES.

Next, we chroot our installation and run mkinitcpio:

# arch-chroot "$root" mkinitcpio -p linux

NBD

The mkinitcpio-nbdAUR package needs to be installed on the client. Build it with makepkg and install it:

# pacman --root "$root" --dbpath "$root/var/lib/pacman" -U mkinitcpio-nbd-0.4-1-any.pkg.tar.xz

You will then need to append nbd to your HOOKS array after net; net will configure your networking for you, but not attempt a NFS mount if nfsroot is not specified in the kernel line.

Client configuration

In addition to the setup mentioned here, you should also set up your hostname, timezone, locale, and keymap, and follow any other relevant parts of the Installation guide.

Bootloader

GRUB

Merge-arrows-2.pngThis article or section is a candidate for merging with GRUB.Merge-arrows-2.png

Notes: (Discuss in Talk:Diskless system#)

Though poorly documented, GRUB supports being loaded via PXE.

# pacman --root "$root" --dbpath "$root/var/lib/pacman" -S grub

Create a grub prefix on the target installation for both architectures using grub-mknetdir.

# arch-chroot "$root" grub-mknetdir --net-directory=/boot --subdir=grub

Luckily for us, grub-mknetdir creates prefixes for all currently compiled/installed targets, and the grub maintainers were nice enough to give us both in the same package, thus grub-mknetdir only needs to be run once.

Now we create a trivial GRUB configuration:

# vim "$root/boot/grub/grub.cfg"
menuentry "Arch Linux" {
    linux /vmlinuz-linux quiet add_efi_memmap ip=:::::eth0:dhcp nfsroot=10.0.0.1:/arch
    initrd /initramfs-linux.img
}

GRUB dark-magic will set root=(tftp,10.0.0.1) automatically, so that the kernel and initramfs are transferred via TFTP without any additional configuration, though you might want to set it explicitly if you have any other non-tftp menuentries.

Note: Modify your kernel line as-necessary, refer to Pxelinux for NBD-related options

Pxelinux

Pxelinux is provided by syslinux, see here for detail.

Additional mountpoints

NBD root

In late boot, you will want to switch your root filesystem mount to both rw, and enable compress=lzo, for much improved disk performance in comparison to NFS.

# vim "$root/etc/fstab"
/dev/nbd0  /  btrfs  rw,noatime,discard,compress=lzo  0 0

Program state directories

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: systemd does not use persistent logging by default when /var/log/journal is in tmpfs and/or does not exist (Discuss in Talk:Diskless system#)

You could mount /var/log, for example, as tmpfs so that logs from multiple hosts do not mix unpredictably, and do the same with /var/spool/cups, so the 20 instances of cups using the same spool do not fight with each other and make 1,498 print jobs and eat an entire ream of paper (or worse: toner cartridge) overnight.

# vim "$root/etc/fstab"
tmpfs   /var/log        tmpfs     nodev,nosuid    0 0
tmpfs   /var/spool/cups tmpfs     nodev,nosuid    0 0

It would be best to configure software that has some sort of state/database to use unique state/database storage directories for each host. If you wanted to run puppet, for example, you could simply use the %H specifier in the puppet unit file:

# vim "$root/etc/systemd/system/puppetagent.service"
[Unit]
Description=Puppet agent
Wants=basic.target
After=basic.target network.target

[Service]
Type=forking
PIDFile=/run/puppet/agent.pid
ExecStartPre=/usr/bin/install -d -o puppet -m 755 /run/puppet
ExecStart=/usr/bin/puppet agent --vardir=/var/lib/puppet-%H --ssldir=/etc/puppet/ssl-%H

[Install]
WantedBy=multi-user.target

Puppet-agent creates vardir and ssldir if they do not exist.

If neither of these approaches are appropriate, the last sane option would be to create a systemd generator that creates a mount unit specific to the current host (specifiers are not allowed in mount units, unfortunately).

Client boot

NBD

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: When using COW on the server, the clients all effectively have read-only mounts of the original filesystem; it should theoretically be safe to do a read-write mount on the NBD server (Discuss in Talk:Diskless system#)

If you are using NBD, you will need to umount the arch.img before/while you boot your client.

This makes things particularly interesting when it comes to kernel updates. You cannot have your client filesystem mounted while you are booting a client, but that also means you need to use a kernel separate from your client filesystem in order to build it.

You will need to first copy $root/boot from the client installation to your tftp root (i.e. /srv/boot).

# cp -r "$root/boot" /srv/boot

You will then need to umount $root before you start the client.

# umount "$root"
Note: To update the kernel in this setup, you either need to mount /srv/boot using NFS in fstab on the client (prior to doing the kernel update) or mount your client filesystem after the client has disconnected from NBD

See also