bug#45444: depmod: ERROR: could not open directory /lib/modules/5.10.2-gnu

bug#45444: depmod: ERROR: could not open directory /lib/modules/5.10.2-gnu

[Jonathan Brielmaier]

depmod doesn't seem to be happy about our paths...

```
# depmod
depmod: ERROR: could not open directory /lib/modules/5.10.2-gnu: No such
file or directory
depmod: FATAL: could not search modules: No such file or directory
```

Happens on up to date master branch:
```
$ guix system describe
Generation 129	Dec 26 2020 11:13:28	(current)
   file name: /var/guix/profiles/system-129-link
   canonical file name: /gnu/store/yb73df860bd39hzrbvhz79ydqyqfbbdh-system
   label: GNU with Linux-Libre 5.10.2
   bootloader: grub
   root device: UUID: d5e47476-ccdb-4dd5-8f69-f670d5ab25a0
   kernel:
/gnu/store/si6ly6im9ih9fpycp5zq1895y2jl4kzm-linux-libre-5.10.2/bzImage
   channels:
     guix:
       repository URL: https://git.savannah.gnu.org/git/guix.git
       branch: master
       commit: 7be871bb69b8df20e566aa3d078b8cbe453693e2
   configuration file:
/gnu/store/gy14nza51q9s8fyhd53caaf0bvv3363w-configuration.scm
```

bug#45444: depmod: ERROR: could not open directory /lib/modules/5.10.2-gnu

[Tobias Geerinckx-Rice via Bug reports for GNU Guix]

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Hi Jonathan,

Jonathan Brielmaier 写道：
> depmod doesn't seem to be happy about our paths...

...and?  :-)

Would I be correct if I guessed that you're using some third-party 
script/how-to that thinks it should run depmod?  That's not 
generally true.  It's also incompatible with (or, irrelevant on) 
Guix by design.  With any system with a read-only root fs, in 
fact.  *points at cloud*  I wonder what depmod does on such 
systems.

  $ sudo depmod -b /run/booted-system/kernel
  depmod: ERROR: 
  openat(/run/booted-system/kernel/lib/modules/5.10.0-r3-16.2429ba5-X230, 
  modules.dep.32260.31994.1609018567, 301, 644): Read-only file 
  system

Followed by about ten more similar errors.  Do we care?  Why?

Thanks for starting the discussion,

T G-R

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