fakeroot(1) Debian manual fakeroot(1)
fakeroot - run a command in an environment faking root privileges for file manipulation
fakeroot [-l|--lib library] [--faked faked-binary] [-i load-file] [-s save-file] [-u|--unknown-is-real ] [-b|--fd-base ] [-h|--help ]
[-v|--version ] [--] [command]
fakeroot runs a command in an environment wherein it appears to have root privileges for file manipulation. This is useful for allowing
users to create archives (tar, ar, .deb etc.) with files in them with root permissions/ownership. Without fakeroot one would need to have
root privileges to create the constituent files of the archives with the correct permissions and ownership, and then pack them up, or one
would have to construct the archives directly, without using the archiver.
fakeroot works by replacing the file manipulation library functions (chmod(2), stat(2) etc.) by ones that simulate the effect the real
library functions would have had, had the user really been root. These wrapper functions are in a shared library /usr/lib/*/libfake-
root-*.so or similar location on your platform. The shared object is loaded through the LD_PRELOAD mechanism of the dynamic loader. (See
If you intend to build packages with fakeroot, please try building the fakeroot package first: the "debian/rules build" stage has a few
tests (testing mostly for bugs in old fakeroot versions). If those tests fail (for example because you have certain libc5 programs on your
system), other packages you build with fakeroot will quite likely fail too, but possibly in much more subtle ways.
Also, note that it's best not to do the building of the binaries themselves under fakeroot. Especially configure and friends don't like it
when the system suddenly behaves differently from what they expect. (or, they randomly unset some environment variables, some of which
-l library, --lib library
Specify an alternative wrapper library.
Specify an alternative binary to use as faked.
Any command you want to be ran as fakeroot. Use '--' if in the command you have other options that may confuse fakeroot's option
Save the fakeroot environment to save-file on exit. This file can be used to restore the environment later using -i. However, this
file will leak and fakeroot will behave in odd ways unless you leave the files touched inside the fakeroot alone when outside the
environment. Still, this can be useful. For example, it can be used with rsync(1) to back up and restore whole directory trees com-
plete with user, group and device information without needing to be root. See /usr/share/doc/fakeroot/README.saving for more
Load a fakeroot environment previously saved using -s from load-file. Note that this does not implicitly save the file, use -s as
well for that behaviour. Using the same file for both -i and -s in a single fakeroot invocation is safe.
Use the real ownership of files previously unknown to fakeroot instead of pretending they are owned by root:root.
-b fd Specify fd base (TCP mode only). fd is the minimum file descriptor number to use for TCP connections; this may be important to avoid
conflicts with the file descriptors used by the programs being run under fakeroot.
-h Display help.
-v Display version.
Here is an example session with fakeroot. Notice that inside the fake root environment file manipulation that requires root privileges
succeeds, but is not really happening.
$ fakeroot /bin/bash
# mknod hda3 b 3 1
# ls -ld hda3
brw-r--r-- 1 root root 3, 1 Jul 2 22:58 hda3
# chown joost:root hda3
# ls -ld hda3
brw-r--r-- 1 joost root 3, 1 Jul 2 22:58 hda3
# ls -ld /
drwxr-xr-x 20 root root 1024 Jun 17 21:50 /
# chown joost:users /
# chmod a+w /
# ls -ld /
drwxrwxrwx 20 joost users 1024 Jun 17 21:50 /
$ ls -ld /
drwxr-xr-x 20 root root 1024 Jun 17 21:50 //
$ ls -ld hda3
-rw-r--r-- 1 joost users 0 Jul 2 22:58 hda3
Only the effects that user joost could do anyway happen for real.
fakeroot was specifically written to enable users to create Debian GNU/Linux packages (in the deb(5) format) without giving them root priv-
ileges. This can be done by commands like dpkg-buildpackage -rfakeroot or debuild -rfakeroot (actually, -rfakeroot is default in debuild
nowadays, so you don't need that argument).
fakeroot is a regular, non-setuid program. It does not enhance a user's privileges, or decrease the system's security.
/usr/lib/*/libfakeroot-*.so The shared library containing the wrapper functions.
The key used to communicate with the fakeroot daemon. Any program started with the right LD_PRELOAD and a FAKEROOTKEY of a running
daemon will automatically connect to that daemon, and have the same "fake" view of the file system's permissions/ownerships.
(assuming the daemon and connecting program were started by the same user).
Fakeroot is implemented by wrapping system calls. This is accomplished by setting LD_LIBRARY_PATH=/usr/lib/fakeroot and
LD_PRELOAD=libfakeroot.so.0. That library is loaded before the system's C library, and so most of the library functions are inter-
cepted by it. If you need to set either LD_LIBRARY_PATH or LD_PRELOAD from within a fakeroot environment, it should be set relative
to the given paths, as in LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/foo/bar/
Every command executed within fakeroot needs to be linked to the same version of the C library as fakeroot itself.
fakeroot doesn't wrap open(), create(), etc. So, if user joost does either
ls -al foo
or the other way around,
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'.
GNU configure (and other such programs)
fakeroot, in effect, is changing the way the system behaves. Programs that probe the system like GNU configure may get confused by
this (or if they don't, they may stress fakeroot so much that fakeroot itself becomes confused). So, it's advisable not to run "con-
figure" from within fakeroot. As configure should be called in the "debian/rules build" target, running "dpkg-buildpackage -rfake-
root" correctly takes care of this.
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).
fakeroot is distributed under the GNU General Public License. (GPL 2.0 or greater).
mostly by J.H.M. Dassen <email@example.com> Rather a lot mods/additions by joost and Clint.
faked(1) dpkg-buildpackage(1), debuild(1) /usr/share/doc/fakeroot/DEBUG
Debian Project 5 October 2014 fakeroot(1)