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

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 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
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>  Rather a lot mods/additions by joost and
       Clint.