man > fakeroot(1)

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|--un‐
       known-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, with‐
       out 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 re‐
       ally 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 fake‐
       root 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 in‐
              formation 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 de‐
       crease 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/owner‐
              ships.  (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 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_LI‐
              BRARY_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 AT debian.org>

       Clint Adams
              <clint AT debian.org>

       Timo Savola

MANUAL PAGE
       mostly by J.H.M. Dassen <jdassen AT 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


Debian Project                             5 October 2014                                fakeroot(1)