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  ar‐
       chives 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 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 pro‐
       grams 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 fake‐
       root. Especially configure and friends don't like it when the system suddenly behaves dif‐
       ferently  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 pretend‐
              ing 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/own‐
              erships.  (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  prob‐
              lems,  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  num‐
              ber  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)