fakeroot(1)                                                Debian manual                                                fakeroot(1)

       fakeroot - run a command in an environment faking root privileges for file manipulation

       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]

       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 ef‐
       fect the real library functions would have had, had the user really been root. These wrapper functions are in a  shared  li‐
       brary  /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).

       -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 fake‐
              root'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 fake‐
              root 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

       -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 im‐
              portant to avoid conflicts with the file descriptors used by the programs being run under fakeroot.

       -h     Display help.

       -v     Display version.

       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
       $ fakeroot /bin/bash
       #  whoami
       # 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).

       fakeroot is a regular, non-setuid program. It does not enhance a user's privileges, or decrease the system's security.

       /usr/lib/*/libfakeroot-*.so The shared library containing the wrapper functions.

              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).


              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  en‐
              vironment, it should be set relative to the given paths, as in LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/foo/bar/

       Library versions
              Every command executed within fakeroot needs to be linked to the same version of the C library as fakeroot itself.

              fakeroot doesn't wrap open(), create(), etc. So, if user joost does either

              touch foo
              ls -al foo

              or the other way around,

              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.

       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).

       fakeroot is distributed under the GNU General Public License.  (GPL 2.0 or greater).

       joost witteveen

       Clint Adams

       Timo Savola

       mostly by J.H.M. Dassen <jdassen@debian.org> Rather a lot mods/additions by joost and Clint.

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

Debian Project                                             5 October 2014                                               fakeroot(1)