Debian manual fakeroot(1) NAME fakeroot - run a command in an environment faking root priv- ileges 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 use- ful for allowing users to create archives (tar, ar, .pkg 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 cor- rect 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* which 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 pack- ages 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 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 Debian Project Last change: 6 August 2004 1 Debian manual fakeroot(1) 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 the file doc/README.saving distributed with the fakeroot source code 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 descrip- tors 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 happen- ing. $ whoami joost $ fakeroot /bin/bash # whoami root # mknod hda3 b 3 1 # ls -ld hda3 Debian Project Last change: 6 August 2004 2 Debian manual fakeroot(1) 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 packages without giving them root privileges. SECURITY ASPECTS fakeroot is a regular, non-setuid program. It does not enhance a user's privileges, or decrease the system's secu- rity. FILES /usr/lib/libfakeroot/libfakeroot.so* The shared library con- taining 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 con- nect 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=lib- fakeroot.so.0. That library is loaded before the sys- tem'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 Debian Project Last change: 6 August 2004 3 Debian manual fakeroot(1) 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 sec- ond 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 unexplain- able 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 `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 con- figure 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 "con- figure" from within fakeroot. Debian Project Last change: 6 August 2004 4 Debian manual fakeroot(1) 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 suc- ceed, 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 Clint Adams Timo Savola MANUAL PAGE mostly by J.H.M. Dassen Rather a lot mods/additions by joost and Clint. SEE ALSO faked(1) ATTRIBUTES See attributes(5) for descriptions of the following attributes: _______________________________________ | ATTRIBUTE TYPE | ATTRIBUTE VALUE| |_______________________________________ | Availability | SUNWfakeroot | |_______________________________________ | Interface Stability| Uncommitted | |____________________|_________________| NOTES Source for fakeroot is available on http://opensolaris.org. Debian Project Last change: 6 August 2004 5