fakeroot

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  li-
       brary  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 them-
       selves 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  op-
              tion 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  out-
              side 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 descrip-
              tor 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 suc-
       ceeds, 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  pro-
              gram  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 ac-
              complished  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 in-
              tercepted  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_LI-
              BRARY_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 unex-
              plainable 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 fake-
              root as small as possible, to limit the  likelihood  of  'colli-
              sions'.

       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  con-
              fused  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  func-
       tions 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/addi-
       tions 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)