1fakeroot(1) Debian manual fakeroot(1)
2
6 fakeroot - run a command in an environment faking root privileges for
7 file manipulation
8
10 fakeroot [-l|--lib library] [--faked faked-binary] [-i load-file] [-s
11 save-file] [-u|--unknown-is-real ] [-b|--fd-base ] [-h|--help ]
12 [-v|--version ] [--] [command]
13
15 fakeroot runs a command in an environment wherein it appears to have
16 root privileges for file manipulation. This is useful for allowing
17 users to create archives (tar, ar, .deb etc.) with files in them with
18 root permissions/ownership. Without fakeroot one would need to have
19 root privileges to create the constituent files of the archives with
20 the correct permissions and ownership, and then pack them up, or one
21 would have to construct the archives directly, without using the
22 archiver.
23 fakeroot works by replacing the file manipulation library functions
25 (chmod(2), stat(2) etc.) by ones that simulate the effect the real
26 library functions would have had, had the user really been root. These
27 wrapper functions are in a shared library /usr/lib/*/libfakeroot-*.so
28 or similar location on your platform. The shared object is loaded
29 through the LD_PRELOAD mechanism of the dynamic loader. (See ld.so(8))
30 If you intend to build packages with fakeroot, please try building the
32 fakeroot package first: the "debian/rules build" stage has a few tests
33 (testing mostly for bugs in old fakeroot versions). If those tests fail
34 (for example because you have certain libc5 programs on your system),
35 other packages you build with fakeroot will quite likely fail too, but
36 possibly in much more subtle ways.
37 Also, note that it's best not to do the building of the binaries them‐
39 selves under fakeroot. Especially configure and friends don't like it
40 when the system suddenly behaves differently from what they expect.
41 (or, they randomly unset some environment variables, some of which
42 fakeroot needs).
43
46 -l library, --lib library
47 Specify an alternative wrapper library.
48 --faked binary
50 Specify an alternative binary to use as faked.
51 [--] command
53 Any command you want to be ran as fakeroot. Use ‘--’ if in the
54 command you have other options that may confuse fakeroot's
55 option parsing.
56 -s save-file
58 Save the fakeroot environment to save-file on exit. This file
59 can be used to restore the environment later using -i. However,
60 this file will leak and fakeroot will behave in odd ways unless
61 you leave the files touched inside the fakeroot alone when out‐
62 side the environment. Still, this can be useful. For example, it
63 can be used with rsync(1) to back up and restore whole directory
64 trees complete with user, group and device information without
65 needing to be root. See /usr/share/doc/fakeroot/README.saving
66 for more details.
67 -i load-file
69 Load a fakeroot environment previously saved using -s from load-
70 file. Note that this does not implicitly save the file, use -s
71 as well for that behaviour. Using the same file for both -i and
72 -s in a single fakeroot invocation is safe.
73 -u, --unknown-is-real
75 Use the real ownership of files previously unknown to fakeroot
76 instead of pretending they are owned by root:root.
77 -b fd Specify fd base (TCP mode only). fd is the minimum file descrip‐
79 tor number to use for TCP connections; this may be important to
80 avoid conflicts with the file descriptors used by the programs
81 being run under fakeroot.
82 -h Display help.
84 -v Display version.
86
89 Here is an example session with fakeroot. Notice that inside the fake
90 root environment file manipulation that requires root privileges suc‐
91 ceeds, but is not really happening.
92 $ whoami
94 joost
95 $ fakeroot /bin/bash
96 # whoami
97 root
98 # mknod hda3 b 3 1
99 # ls -ld hda3
100 brw-r--r-- 1 root root 3, 1 Jul 2 22:58 hda3
101 # chown joost:root hda3
102 # ls -ld hda3
103 brw-r--r-- 1 joost root 3, 1 Jul 2 22:58 hda3
104 # ls -ld /
105 drwxr-xr-x 20 root root 1024 Jun 17 21:50 /
106 # chown joost:users /
107 # chmod a+w /
108 # ls -ld /
109 drwxrwxrwx 20 joost users 1024 Jun 17 21:50 /
110 # exit
111 $ ls -ld /
112 drwxr-xr-x 20 root root 1024 Jun 17 21:50 //
113 $ ls -ld hda3
114 -rw-r--r-- 1 joost users 0 Jul 2 22:58 hda3
115 Only the effects that user joost could do anyway happen for real.
117 fakeroot was specifically written to enable users to create Debian
119 GNU/Linux packages (in the deb(5) format) without giving them root
120 privileges. This can be done by commands like dpkg-buildpackage
121 -rfakeroot or debuild -rfakeroot (actually, -rfakeroot is default in
122 debuild nowadays, so you don't need that argument).
123
125 fakeroot is a regular, non-setuid program. It does not enhance a user's
126 privileges, or decrease the system's security.
127
129 /usr/lib/*/libfakeroot-*.so The shared library containing the wrapper
130 functions.
131
133 FAKEROOTKEY
134 The key used to communicate with the fakeroot daemon. Any pro‐
135 gram started with the right LD_PRELOAD and a FAKEROOTKEY of a
136 running daemon will automatically connect to that daemon, and
137 have the same "fake" view of the file system's permissions/own‐
138 erships. (assuming the daemon and connecting program were
139 started by the same user).
140 LD_LIBRARY_PATH
142 LD_PRELOAD
144 Fakeroot is implemented by wrapping system calls. This is
145 accomplished by setting LD_LIBRARY_PATH=/usr/lib/fakeroot and
146 LD_PRELOAD=libfakeroot.so.0. That library is loaded before the
147 system's C library, and so most of the library functions are
148 intercepted by it. If you need to set either LD_LIBRARY_PATH or
149 LD_PRELOAD from within a fakeroot environment, it should be set
150 relative to the given paths, as in
151 LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/foo/bar/
152
155 Library versions
156 Every command executed within fakeroot needs to be linked to the
157 same version of the C library as fakeroot itself.
158 open()/create()
160 fakeroot doesn't wrap open(), create(), etc. So, if user joost
161 does either
162 touch foo
164 fakeroot
165 ls -al foo
166 or the other way around,
168 fakeroot
170 touch foo
171 ls -al foo
172 fakeroot has no way of knowing that in the first case, the owner
174 of foo really should be joost while the second case it should
175 have been root. For the Debian packaging, defaulting to giving
176 all "unknown" files uid=gid=0, is always OK. The real way around
177 this is to wrap open() and create(), but that creates other
178 problems, as demonstrated by the libtricks package. This package
179 wrapped many more functions, and tried to do a lot more than
180 fakeroot . It turned out that a minor upgrade of libc (from one
181 where the stat() function didn't use open() to one with a stat()
182 function that did (in some cases) use open()), would cause unex‐
183 plainable segfaults (that is, the libc6 stat() called the
184 wrapped open(), which would then call the libc6 stat(), etc).
185 Fixing them wasn't all that easy, but once fixed, it was just a
186 matter of time before another function started to use open(),
187 never mind trying to port it to a different operating system.
188 Thus I decided to keep the number of functions wrapped by fake‐
189 root as small as possible, to limit the likelihood of ‘colli‐
190 sions’.
191 GNU configure (and other such programs)
193 fakeroot, in effect, is changing the way the system behaves.
194 Programs that probe the system like GNU configure may get con‐
195 fused by this (or if they don't, they may stress fakeroot so
196 much that fakeroot itself becomes confused). So, it's advisable
197 not to run "configure" from within fakeroot. As configure should
198 be called in the "debian/rules build" target, running
199 "dpkg-buildpackage -rfakeroot" correctly takes care of this.
200
202 It doesn't wrap open(). This isn't bad by itself, but if a program does
203 open("file", O_WRONLY, 000), writes to file "file", closes it, and then
204 again tries to open to read the file, then that open fails, as the mode
205 of the file will be 000. The bug is that if root does the same, open()
206 will succeed, as the file permissions aren't checked at all for root. I
207 choose not to wrap open(), as open() is used by many other functions in
208 libc (also those that are already wrapped), thus creating loops (or
209 possible future loops, when the implementation of various libc func‐
210 tions slightly change).
211
213 fakeroot is distributed under the GNU General Public License. (GPL 2.0
214 or greater).
215
217 joost witteveen
218 <joostje@debian.org>
219 Clint Adams
221 <clint@debian.org>
222 Timo Savola
224
226 mostly by J.H.M. Dassen <jdassen@debian.org> Rather a lot mods/addi‐
227 tions by joost and Clint.
228
230 faked(1) dpkg-buildpackage(1), debuild(1) /usr/share/doc/fakeroot/DEBUG
231Debian Project 5 October 2014 fakeroot(1)