[BUG?] rootdelay with nfs root

kokoko3k · 2013-05-24 06:12:42

I've a pxe system that mounts "/" over nfs, and i noticed that the 10 seconds the system waits for /dev/nfs always timeout, on every boot.
but after that, the system boots fine and the nfs mounts are available.
changing rootdelay kernel parameter to a lower value (even just 1 second) , makes the system boots faster and fine;
so it seems that for nfs roots, the system is not aware of when the filesystem is available, and it just wait for the entire rootdelay time.
is this expected?

thanks

Last edited by kokoko3k (2013-05-24 11:10:08)

WonderWoofy · 2013-05-24 07:38:26

Instead of using the kernel's rootdelay parameter, have you thought about using rootwait? Or better yet, since you are using the initamfs to boot this NFS share, you should probably be using the "sleep" hook for mkinitcpio. This will allow you to either use a simple "sleep=<time>" or probably more appropriately, "sleepdevice=<device node>".

I think the rootdelay and rootwait parameters are for when the kernel is booting w/o an initramfs. I could be totally wrong, but this is the impression that i have gotten in the past.

kokoko3k · 2013-05-24 08:31:36

I wasn't clear enough.
For my nfs root, rootdelay (which defaults to 10 secs if not speicifed otherwise), acts exactly like the sleep hook.
I mean, i don't need the system to wait 10 seconds.

this is the boot line for pxelinux:

default menu.c32
prompt 0
timeout 2
ONTIMEOUT arch

MENU TITLE Main Menu

LABEL arch
        MENU LABEL ArchLinux
        kernel /archlinux/boot/vmlinuz-linux
        append initrd=archlinux/boot/initramfs-linux-fallback.img rootfstype=nfs root=/dev/nfs nfsroot=192.168.117.244:/home/tftproot/archlinux/,rsize=16384,wsize=16384 ip=::::::dhcp  init=/usr/lib/systemd/systemd rootdelay=1

If i omit the rootdelay parameter, the system waits 10 seconds and boots fine.
If i specify rootdelay=1, it just wait 1 second, and boots fine too.

The question is... how can tell him to boot as soon as nfs is available without useless delays?

Last edited by kokoko3k (2013-05-24 08:55:22)

kokoko3k · 2013-05-24 11:09:53

Update:
I went deeper into this,
The problem is (seems to be) that the init function: poll_device() in /usr/lib/initcpio/init_functions,
waits for the device /dev/nfs (specified in the kernel command line) to be available.
But /dev/nfs will never show up because:

https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt wrote:

root=/dev/nfs
This is necessary to enable the pseudo-NFS-device. Note that it's not a
real device but just a synonym to tell the kernel to use NFS instead of
a real device.

To make the long story short:
- the kernel needs root=/dev/nfs in order to boot from nfs
- arch init waits for /dev/nfs
- /dev/nfs does not appear because is not meant to be a real device

1) Is this a bug in the arch init system or am i missing something?
2) Is it safe to put rootdelay=0 so that nfsmount waits for the mount to appear or i could risk that the system will not boot?

by now rootdelay=0 works, but i'm pushing that nfs exports to about 60 clients, so i need to be sure.

Thanks.

Last edited by kokoko3k (2013-05-24 11:12:41)

manio · 2024-10-12 08:03:54

@kokoko3k
Any issues with this rootdelay=0 ?
I was waiting 10 seconds for nothing every boot for years (hopefully I am not rebooting very often), but yesterday I upgraded from NFSv3 to NFSv4 and I also decided to put this in kernel commandline.
So far it seems that it is working OK. It's waiting about 1-2sec instead of 10 !

WorMzy · 2024-10-12 16:09:38

Mod note: closing this old thread.

https://wiki.archlinux.org/title/Genera … bumping%22

Arch Linux

#1 2013-05-24 06:12:42

[BUG?] rootdelay with nfs root

#2 2013-05-24 07:38:26

Re: [BUG?] rootdelay with nfs root

#3 2013-05-24 08:31:36

Re: [BUG?] rootdelay with nfs root

#4 2013-05-24 11:09:53

Re: [BUG?] rootdelay with nfs root

#5 2024-10-12 08:03:54

Re: [BUG?] rootdelay with nfs root

#6 2024-10-12 16:09:38

Re: [BUG?] rootdelay with nfs root

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