NAME¶
fakeroot - run a command in an environment faking root privileges for file
manipulation
SYNOPSIS¶
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]
DESCRIPTION¶
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/libfakeroot.so* which is
loaded through the
LD_PRELOAD mechanism of the dynamic loader. (See
ld.so(8))
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 fakeroot needs).
OPTIONS¶
- -l library, --lib library
- Specify an alternative wrapper library.
- --faked binary
- Specify an alternative binary to use as faked.
- [--] command
- Any command you want to be ran as fakeroot. Use
‘--’ if in the command you have other options that may confuse
fakeroot's option parsing.
- -s save-file
- 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 complete with user, group and
device information without needing to be root. See
/usr/share/doc/fakeroot/README.saving for more details.
- -i load-file
- 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.
- -u, --unknown-is-real
- 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.
EXAMPLES¶
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.
$ whoami
joost
$ fakeroot /bin/bash
# whoami
root
# 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 /
# exit
$ 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
privileges. 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).
SECURITY ASPECTS¶
fakeroot is a regular, non-setuid program. It does not enhance a user's
privileges, or decrease the system's security.
FILES¶
/usr/lib/libfakeroot/libfakeroot.so* The shared library containing the
wrapper functions.
ENVIRONMENT¶
- FAKEROOTKEY
- 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).
- LD_LIBRARY_PATH
- LD_PRELOAD
- 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 intercepted 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/
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’.
- 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
"configure" from within fakeroot. As configure should be called
in the "debian/rules build" target, running
"dpkg-buildpackage -rfakeroot" correctly takes care of
this.
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).
COPYING¶
fakeroot is distributed under the GNU General Public License. (GPL 2.0 or
greater).
AUTHORS¶
- joost witteveen
- <joostje@debian.org>
- Clint Adams
- <clint@debian.org>
- Timo Savola
MANUAL PAGE¶
mostly by J.H.M. Dassen <jdassen@debian.org> Rather a lot mods/additions
by joost and Clint.
SEE ALSO¶
faked(1)
dpkg-buildpackage(1),
debuild(1)
/usr/share/doc/fakeroot/DEBUG