fakeroot(1)			 Debian manual			   fakeroot(1)

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
       or similar location on your platform.  The shared object 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 run 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-*.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> with rather a lot of
       modsifications and additions by joost and Clint.

SEE ALSO
       debuild(1), dpkg-buildpackage(1), faked(1),
       /usr/share/doc/fakeroot/DEBUG

Debian Project			  2024-12-19			   fakeroot(1)