Last Change: 2018-09-07, 16:50
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fakeroot − utför ett kommando i en miljö som fejkar root−privilegier för filmanipulation
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 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))
Om du planerar att bygga paket med hjälp av fakeroot, försök först att bygga fakeroot−paketet: "debian/rules build"−stadiet har ett par tester (som mestadels testar efter buggar i gamla versioner av fakeroot). Om dessa tester misslyckas (till exempel på grund av att du har vissa libc5−program på ditt system) så är det troligt att du också kommer att misslyckas bygga andra paket, och det är möjligt att dessa fel blir betydligt svårare att hitta.
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
Ange ett alternativt bibliotek med ersättningsfunktioner.
−−faked binär
Ange en alternativ binär att använda istället för faked(1).
[−−] kommando
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.
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−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. |
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−h |
Display help. |
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−v |
Display version. |
Här är ett exempel på hur fakeroot kan användas. Notera att i den fejkade root−miljön så lyckas filmanipulering som kräver root−privilegier, trots att den egentligen inte utförs.
$ 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
Enbart de operationer som användaren joost skulle kunna ha genomfört som sig själv utförs på riktigt.
fakeroot skrevs speciellt i syfte att ge användare möjlighet att skapa Debian GNU/Linux−paket (i deb(5) format) utan att behöva root−privilegier. Detta kan utföras genom kommandon såsom dpkg−buildpackage −rfakeroot eller debuild −rfakeroot (−rfakeroot är numera standard i debuild, så du behöver inte ens använda den parametern).
fakeroot är ett vanligt program utan setuid. Det ger inte användaren några extra privilegier, och minskar inte systemets säkerhet.
/usr/lib/*/libfakeroot−*.so The shared library containing the wrapper functions.
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/
Biblioteksversioner
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
eller omvänt,
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 (och liknande program)
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 distribueras under GNU General Public License. (GPL 2.0 eller senare).
joost witteveen
<joostje AT debian DOT org>
Clint Adams
<clint AT debian DOT org>
Timo Savola
David Weinehall <taoATkernelDOTorg>
mostly by J.H.M. Dassen <jdassen AT debian DOT org> Rather a lot mods/additions by joost and Clint.
faked(1) dpkg−buildpackage(1), debuild(1) /usr/share/doc/fakeroot/DEBUG