Arch Linux

FIRST the bug report I almost submitted for pacman, before figuring out it is a pacstrap bug

Nfs-server machine already has /var/cache/pacman/pkg and /var/lib/pacman/sync. I want to nfs mount these to other systems running the live ISO, so up-to-date packages already in my internal network aren't downloaded from the public mirrors. (I will also be nfs mounting my local repository which has built AUR packages, which is what drove me to this point, but that's left out of this bug report as not needed.)

Saw quite a few people saying they've done this, but it wasn't working for me.

Turns out this works:
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(these commands on the live Arch ISO, no partitions for reduced test-case, assuming 192.168.1.2 has the shares)
mkfs.btrfs -f /dev/vda
mount /dev/vda /mnt
mkdir -p /mnt/var/cache/pacman/pkg
mount 192.168.1.2:/var/cache/pacman/pkg /mnt/var/cache/pacman/pkg
mkdir -p /mnt/var/lib/pacman/sync
mount 192.168.1.2:/var/lib/pacman/sync /mnt/var/lib/pacman/sync
pacstrap -d /mnt man-pages
umount /mnt/var/cache/pacman/pkg
umount /mnt/var/lib/pacman/sync
umount /mnt
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But, this does not work:
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mkfs.btrfs -f /dev/vda
mount /dev/vda /mnt
mkdir /mnt/root
mkdir -p /mnt/root/var/cache/pacman/pkg
mount 192.168.1.2:/var/cache/pacman/pkg /mnt/root/var/cache/pacman/pkg
mkdir -p /mnt/root/var/lib/pacman/sync
mount 192.168.1.2:/var/lib/pacman/sync /mnt/root/var/lib/pacman/sync
pacstrap -d /mnt/root man-pages
umount /mnt/root/var/cache/pacman/pkg
umount /mnt/root/var/lib/pacman/sync
rm -r /mnt/root
umount /mnt
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The ONLY difference between these lists of commands is the first one uses /mnt as the new root, and the second one uses /mnt/root, where /mnt is the mountpoint. Im my actual case, /mnt is a btrfs volume and /mnt/root is a btrfs subvolume that will be mounted as root in the system being installed. But, I removed btrfs from the test scenario because I found it acts the same way whether it's a btrfs subvolume directory or just a normal directory.

I'm just installing "man-pages" with pacstrap in these test cases, because that's a base package that has no dependencies. (Quicker testing.)

By this "works", for the first list, I mean that pacman says core/extra/community is up to date (assuming that they are - i.e. that the nfs-server has refreshed them recently) and installs man-pages without downloading it.

By this "does not work", for the second list, yes, it technically installs. But, my point is that pacman downloads the package databases from scratch, and downloads man-pages from one of the official mirrors, when it should be doing neither.


If I install strace in the live Arch ISO environment (so not using /mnt or pacstrap), and edit /usr/bin/pacstrap:361 from "pacman -r..." to "strace pacman -r..." and re-run the second list, above, and add to pacstrap "> pacs 2>&1", I see in the pacs output file unexpected ENOENT's, including:

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access("/mnt/root/var/lib/pacman/sync/core.db", R_OK) = -1 ENOENT (No such file or directory)
stat("/mnt/root/var/cache/pacman/pkg/man-pages-4.02-1-any.pkg.tar.xz", 0x7ffd71225070) = -1 ENOENT (No such file or directory)
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But these files very much exist: (before I perform the umount's in the lists above)
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# ll /mnt/root/var/cache/pacman/pkg/man-pages*
-rw-r--r-- 1 root root 5669120 Aug 11 16:42 /mnt/root/var/cache/pacman/pkg/man-pages-4.02-1-any.pkg.tar.xz
# ll /mnt/root/var/lib/pacman/sync/core.db
-rw-r--r-- 1 root root 124041 Aug 28 18:33 /mnt/root/var/lib/pacman/sync/core.db
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NOW to show this is a pacstrap bug, not pacman...

Re-ran these two lists, except ran pacstrap through "bash -x " to get bash debug output, redirecting each list to a separate output file. Edited the second list's file, and replaced "/mnt/root" with "/mnt" to eliminate the expected differences, and see what the unexpected differences were, if any. I then saw these entries, which are listed below in their original form (not my search-replace form):

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chroot_add_mount /mnt/root /mnt/root --bind
mount /mnt/root /mnt/root --bind
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If in the archiso console I have the nfs directories mounted, then this shows these commands are the issue because:

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# ll /mnt/root/var/cache/pacman/pkg | wc -l
243
# mount /mnt/root /mnt/root --bind
# ll /mnt/root/var/cache/pacman/pkg | wc -l
1
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The command "mount /mnt/root /mnt/root --bind" hides the nfs mounts.

So, I think the bug is in pacstrap's chroot_maybe_add_mount(). Unless this is a bug in mount, not sure what the expected behavior of this command would be... But even still, pacstrap could guard against it.