Thank you for taking the time to report this bug and helping to make
Ubuntu better.
This is interesting and I appreciate your investigation! I wonder though
if there's a third outcome here - that it's not a bug because the glibc
implementation of lchmod() requires /proc to be mounted, and if you
don't have /proc mounted then by that definition you have a broken
system and lchmod() is not expected to work, so rsync won't work, as a
design decision of upstream glibc.
I'm not claiming that this is the case, just that it's another case to
consider.
** Changed in: rsync (Ubuntu)
Status: New => Triaged
** Summary changed:
- rsync uses lchmod and fails in Ubuntu >= 20.10
+ rsync uses lchmod and fails in Ubuntu >= 20.10 if /proc isn't mounted
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https://bugs.launchpad.net/bugs/1902109
Title:
rsync uses lchmod and fails in Ubuntu >= 20.10 if /proc isn't mounted
Status in rsync package in Ubuntu:
Triaged
Bug description:
Rsync in Ubuntu 20.10 fails when /proc isn't mounted, while it worked before.
This happens because AC_CHECK_FUNC(lchmod) returns "yes" in 20.10, while it
returned "no" before.
Steps to reproduce:
# Emulate /proc not being mounted
$ mount --bind / /mnt
$ chroot /mnt rsync -a /bin/ls .
rsync: [receiver] failed to set permissions on "/.ls.CDExhu": Operation not
supported (95)
rsync error: some files/attrs were not transferred (see previous errors)
(code 3) at main.c(1330) [sender=3.2.3]
I reported this issue upstream in
https://github.com/WayneD/rsync/issues/109 but the rsync developer
says it's a problem in libc, and it might well be.
Simple C code to reproduce the problem without rsync:
printf("lchmod returned: %d\n", lchmod("/tmp/ls", 0755));
If /tmp/ls is e.g. mode=0123, and needs to be changed, lchmod fails
when /proc isn't mounted, yet it succeeds if it is mounted.
Python had a similar issue, and they ended up avoiding
AC_CHECK_FUNC(lchmod) under Linux:
https://bugs.python.org/issue34652
https://github.com/python/cpython/commit/69e96910153219b0b15a18323b917bd74336d229#diff-49473dca262eeab3b4a43002adb08b4db31020d190caaad1594b47f1d5daa810R3140
```c
if test "$MACHDEP" != linux; then
AC_CHECK_FUNC(lchmod)
fi
```
So I'm not sure which package is causing the bug here. Should autoconf
return false? Should libc implement lchown without the bug? Or should
rsync skip lchmod under Linux, like python did?
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