Saluton!
Ivan Vilata i Balaguer <i...@selidor.net> skribis:
> Ivan Vilata i Balaguer (2019-11-01 11:10:02 -0400) wrote:
>
>> Ludovic Courtès (2019-11-01 15:26:27 +0100) wrote:
>>
>> > […] What about a read-only bind mount like this:
>> >
>> > unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt
>> >
>> > ?
>>
>> This one looks more interesting:
>>
>> $ unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt && echo ok
>> mount: /tmp/tt: filesystem was mounted, but any subsequent operation
>> failed: Unknown error 5005.
>> $ echo $?
>> 32
>
> BTW, I ran that under strace and it looks like the read-only remount fails
> after mounting `/var/run/nscd` in the new namespace has succeeded:
>
> $ strace -f unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt
> […]
> access("/run/mount", R_OK|W_OK) = -1 EACCES (Permission denied)
> mount("/run/nscd", "/tmp/tt", 0x14c25b0, MS_RDONLY|MS_BIND, NULL) = 0
> mount("none", "/tmp/tt", NULL, MS_RDONLY|MS_REMOUNT|MS_BIND, NULL) = -1
> EPERM (Operation not permitted)
> write(2, "mount: ", 7mount: ) = 7
> write(2, "/tmp/tt: filesystem was mounted,"..., 89/tmp/tt: filesystem was
> mounted, but any subsequent operation failed: Unknown error 5005.) = 89
> write(2, "\n", 1
> […]
Weird, why does it remount it?
What does:
mount | grep /run
returns? I just tried on a Debian 10 image with Linux 4.19.0 and /run
is a tmpfs, which may be the reason why read-only bind-mounts fail (or
at least there’s a bug in that area.)
Anyway, below is a patch for you to test. Let me know how it goes. :-)
Thanks,
Ludo’.
diff --git a/gnu/system/file-systems.scm b/gnu/system/file-systems.scm
index 6cf6ccc53e..6cdb2b749d 100644
--- a/gnu/system/file-systems.scm
+++ b/gnu/system/file-systems.scm
@@ -507,7 +507,8 @@ a bind mount."
;; XXX: On some GNU/Linux systems, /etc/resolv.conf is a
;; symlink to a file in a tmpfs which, for an unknown reason,
;; cannot be bind mounted read-only within the container.
- (writable? (string=? file "/etc/resolv.conf"))))
+ (writable? (or (string=? file "/etc/resolv.conf")
+ (string=? file "/var/run/nscd")))))
(cons "/var/run/nscd" %network-configuration-files)))
(define (file-system-type-predicate type)
