fakeroot cdebootstrap: Failed to unshare: Operation not permitted [duplicate]

Question

On Debian, when running:

$ fakeroot cdebootstrap stable /tmp/foo

cdebootstrap downloads the packages, but when it has to extract them, I get this error:

E: Failed to unshare: Operation not permitted

How can I run cdebootstrap as non-root?

This part in unshare's manual seems relevant, but am not sure how:

EPERM (since Linux 3.9)
              CLONE_NEWUSER was specified in flags and the caller is in a
              chroot environment (i.e., the caller's root directory does not
              match the root directory of the mount namespace in which it
              resides).

Answer 1

Problem

Your issue has to do with permission inheritance. cdbootstrap will inherit the permissions of fakeroot, which can be elevated via sudo. Issue:

sudo fakeroot cdbootstrap /tmp/foo

If the above command succeeds, permissions on /tmp are the issue. See What are common rights for /tmp ? I unintentionally set it all public recursively, for what the default permissions should be. Generally, writing anything into /tmp that wasn't put there by an application is a bad idea, and fakeroot has its own issues. From the man page:

LIMITATIONS

Library versions

Every command executed within fakeroot needs to be linked to the same version of the C library as fakeroot itself.

open()/create()

fakeroot doesn't wrap open(), create(), etc. So, if user joost does either

  touch foo
  fakeroot
  ls -al foo

or the other way around,

  fakeroot
  touch foo
  ls -al foo

fakeroot has no way of knowing that in the first case, the owner
of foo really should be joost while the second case it should
have been root. For the Debian packaging, defaulting to giving
all "unknown" files uid=gid=0, is always OK. The real way around
this is to wrap open() and create(), but that creates other
problems, as demonstrated by the libtricks package. This package
wrapped many more functions, and tried to do a lot more than
fakeroot . It turned out that a minor upgrade of libc (from one
where the stat() function didn't use open() to one with a stat() function that did (in some cases) use open()), would cause unexplainable segfaults (that is, the libc6 stat() called the wrapped open(), which would then call the libc6 stat(), etc).
Fixing them wasn't all that easy, but once fixed, it was just a
matter of time before another function started to use open(),
never mind trying to port it to a different operating system.
Thus I decided to keep the number of functions wrapped by fakeroot as small as possible, to limit the likelihood of 'collisions'.

BUGS

It doesn't wrap open(). This isn't bad by itself, but if a program does open("file", O_WRONLY, 000), writes to file "file", closes it, and then again tries to open to read the file, then that open fails, as the mode of the file will be 000. The bug is that if root does the same, open() will succeed, as the file permissions aren't checked at all for root. I choose not to wrap open(), as open() is used by many other functions in libc (also those that are already wrapped), thus creating loops (or possible future loops, when the implementation of various libc functions slightly change).

---

Better Solution

Instead of using privilege escalation to achieve what you're trying to do consider using a proper chroot, as outlined in the DebootstrapChroot Documentation for Ubuntu, or the Official Debian Documentation for DebBootStrap.

Answer 2

maybe /tmp is the issue. try

$fakeroot cdebootstrap stable $HOME/somedir