Using nix-store --restore to install sources - nix

Question

I'm trying to install mythtv on nixOS.
mythtv uses Qt which uses tremor from xiph.org . git.xiph.org is currently unresponsive, so the install fails. Using nix show-derivation on the relevant .drv file, I see
{
"/nix/store/srhlr1v02a1gkp1ld1hrjzda0kfjcjkf-tremor-562307a.drv": {
"outputs": {
"out": {
"path": "/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a",
"hashAlgo": "r:sha256",
"hash": "f80ffaf1dc452061c4a2e7566ccec5f8ec1496ef2894857ed42f3ef7097e0754"
}
},
"inputSrcs": [
"/nix/store/jr7l8xyyanakpqr954rvj58lyqal1vfb-builder.sh",
"/nix/store/m9n5a7g5nb7jglcs9i58ycrkmn998wrp-nix-prefetch-git"
],
...
"env": {
...
"url": "https://git.xiph.org/tremor.git"
}
}
}
So I looked for, and succesfully found, this in cache.nixos.org:
$ curl cache.nixos.org/aq8d6qgp55w0g9xdb81cys9b3l95d7hb.narinfo
StorePath: /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
URL: nar/0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz
Compression: xz
FileHash: sha256:0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa
FileSize: 109380
NarHash: sha256:0m07gq4zfgigsiz8b518xyb19v7qqp76qmp7lb262825vkqzl3zq
NarSize: 588216
References:
Deriver: cr4d6v24rchmkv26mvzlzrr23z7a5ghb-tremor-562307a.drv
Sig: cache.nixos.org-1:rb9+9oe3LMRlh8TbLuZ7nhMaPIc5fwrAhG4tXtBLAgd7EGBoS2jk6BgYzSRI49MgwdPgAKTtzM3W0Wj0jGojDQ==
Then, I downloaded the narchive: curl -O cache.nixos.org/nar/0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz and attempted to restore it: nix-store --restore /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a < <(xzdec 0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz).
This fails initially because the directory exists:
$ nix-store --restore /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a < <(xzdec 0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz)
error: creating directory '/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a': File exists
$ ls -ld /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
drwxr-xr-x 3 nixbld10 nixbld 18 Jun 8 20:57 /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
$ ls -l /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
total 0
So I delete it, and try again:
$ nix-store --delete /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
finding garbage collector roots...
removing stale link from '/nix/var/nix/gcroots/auto/f9ldmvya8mix2j52cwsl8h0rqvjycjjy' to '/tmp/martyn/nixos-rebuild.didhrl/nix.drv'
removing stale link from '/nix/var/nix/gcroots/auto/qs606yn37b7irq7jmkvj0ld9wjv36fma' to '/tmp/martyn/nixos-rebuild.didhrl/nix'
deleting '/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a'
deleting '/nix/store/trash'
deleting unused links...
note: currently hard linking saves 0.00 MiB
1 store paths deleted, 0.07 MiB freed
$ nix-store --restore /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a < <(xzdec 0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz)
error: creating directory '/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a': Permission denied
I find that "permission denied" to be a bit odd - I have normal rights to install, indeed to delete (above)...
But it's okay, I can do this with sudo: ```$ sudo nix-store --restore /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a < <(xzdec 0jm68cws51814dm7gks62vj7a8zrdhwv2x364kq78wbkkqh58maa.nar.xz)
$ ls -ld /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
drwxr-xr-x 5 root root 4096 Jun 9 07:27 /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
$ ls -l !$ | head
$ ls -l /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a | head
total 496
-rw-r--r-- 1 root root 6534 Jun 9 07:27 asm_arm.h
-rwxr-xr-x 1 root root 3657 Jun 9 07:27 autogen.sh
-rw-r--r-- 1 root root 4639 Jun 9 07:27 backends.h
-rw-r--r-- 1 root root 14547 Jun 9 07:27 block.c
-rw-r--r-- 1 root root 1109 Jun 9 07:27 block.h
-rw-r--r-- 1 root root 467 Jun 9 07:27 CHANGELOG
-rw-r--r-- 1 root root 10765 Jun 9 07:27 codebook.c
-rw-r--r-- 1 root root 4078 Jun 9 07:27 codebook.h
-rw-r--r-- 1 root root 3084 Jun 9 07:27 codec_internal.h
Better still, the hash looks good:
$ nix-hash /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a --type sha256
f80ffaf1dc452061c4a2e7566ccec5f8ec1496ef2894857ed42f3ef7097e0754
I notice that a lock file remains, so I delete that:
Along the way, I noticed that after the restore, the lock file remains:
$ ls -l /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a.lock
-rw------- 1 root root 0 May 27 08:15 /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a.lock
$ nix-store --delete !$
$ nix-store --delete /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a.lock
finding garbage collector roots...
deleting '/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a.lock'
deleting '/nix/store/trash'
deleting unused links...
note: currently hard linking saves 0.00 MiB
1 store paths deleted, 0.00 MiB freed
So I should be all set? It seems not:
$ nix-env -i /nix/store/srhlr1v02a1gkp1ld1hrjzda0kfjcjkf-tremor-562307a.drv
installing 'tremor-562307a.drv'
these derivations will be built:
/nix/store/srhlr1v02a1gkp1ld1hrjzda0kfjcjkf-tremor-562307a.drv
building '/nix/store/srhlr1v02a1gkp1ld1hrjzda0kfjcjkf-tremor-562307a.drv'...
exporting https://git.xiph.org/tremor.git (rev 562307a4a7082e24553f3d2c55dab397a17c4b4f) into /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
Initialized empty Git repository in /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a/.git/
I am baffled why nix is rebuilding a store path that is extant and has the requested hash.
I tried repairing the path, to see if maybe the database needed updating in some way:
$ nix-store --repair-path /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
error: you don't have sufficient rights to use this command
$ sudo nix-store --repair-path /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a
error: path '/nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a' is not valid
$ nix-hash /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a --type sha256
f80ffaf1dc452061c4a2e7566ccec5f8ec1496ef2894857ed42f3ef7097e0754
So that 'path ... is not valid' is alarming, but still, it's present with a good hash, so I don't understand why it's supposedly not valid, nor why nix insists on rebuilding it.

Answer 1

Maybe you have a negative narinfo cache entry or maybe the derivation prefers a local build. You could try
nix-store --delete /nix/store/srhlr1v02a1gkp1ld1hrjzda0kfjcjkf-tremor-562307a.drv
nix-store --realise --option narinfo-cache-negative-ttl 0 -vvvvv /nix/store/aq8d6qgp55w0g9xdb81cys9b3l95d7hb-tremor-562307a