1PKEXEC(1) pkexec PKEXEC(1)
2
6 pkexec - Execute a command as another user
7
9 pkexec [--version] [--disable-internal-agent] [--help]
10 pkexec [--user username] PROGRAM [ARGUMENTS...]
12
14 pkexec allows an authorized user to execute PROGRAM as another user. If
15 PROGRAM is not specified, the default shell will be run. If username is
16 not specified, then the program will be executed as the administrative
17 super user, root.
18
20 Upon successful completion, the return value is the return value of
21 PROGRAM. If the calling process is not authorized or an authorization
22 could not be obtained through authentication or an error occured,
23 pkexec exits with a return value of 127. If the authorization could not
24 be obtained because the user dismissed the authentication dialog,
25 pkexec exits with a return value of 126.
26
28 pkexec, like any other polkit application, will use the authentication
29 agent registered for the calling process or session. However, if no
30 authentication agent is available, then pkexec will register its own
31 textual authentication agent. This behavior can be turned off by
32 passing the --disable-internal-agent option.
33
35 Executing a program as another user is a privileged operation. By
36 default the action to check for (see the section called “ACTION AND
37 AUTHORIZATIONS”) requires administrator authentication. In addition,
38 the authentication dialog presented to the user will display the full
39 path to the program to be executed so the user is aware of what will
40 happen.
41 The environment that PROGRAM will run it, will be set to a minimal
43 known and safe environment in order to avoid injecting code through
44 LD_LIBRARY_PATH or similar mechanisms. In addition the PKEXEC_UID
45 environment variable is set to the user id of the process invoking
46 pkexec. As a result, pkexec will not by default allow you to run X11
47 applications as another user since the $DISPLAY and $XAUTHORITY
48 environment variables are not set. These two variables will be retained
49 if the org.freedesktop.policykit.exec.allow_gui annotation on an action
50 is set to a nonempty value; this is discouraged, though, and should
51 only be used for legacy programs.
52 Note that pkexec does no validation of the ARGUMENTS passed to PROGRAM.
54 In the normal case (where administrator authentication is required
55 every time pkexec is used), this is not a problem since if the user is
56 an administrator he might as well just run pkexec bash to get root.
57 However, if an action is used for which the user can retain
59 authorization (or if the user is implicitly authorized) this could be a
60 security hole. Therefore, as a rule of thumb, programs for which the
61 default required authorization is changed, should never implicitly
62 trust user input (e.g. like any other well-written suid program).
63
65 By default, the org.freedesktop.policykit.exec action is used. To use
66 another action, use the org.freedesktop.policykit.exec.path annotation
67 on an action with the value set to the full path of the program. In
68 addition to specifying the program, the authentication message,
69 description, icon and defaults can be specified. If the
70 org.freedesktop.policykit.exec.argv1 annotation is present, the action
71 will only be picked if the first argument to the program matches the
72 value of the annotation.
73 Note that authentication messages may reference variables (see the
75 section called “VARIABLES”), for example $(user) will be expanded to
76 the value of the user variable.
77
79 To avoid modifying existing software to prefix their command-line
80 invocations with pkexec, it's possible to use pkexec in a she-bang
81 wrapper[1] like this:
82 #!/usr/bin/pkexec /usr/bin/python
84 import os
86 import sys
87 print "Hello, I'm running as uid %d"%(os.getuid())
89 for n in range(len(sys.argv)):
91 print "arg[%d]=`%s'"%(n, sys.argv[n])
92 If this script is installed into /usr/bin/my-pk-test, then the
94 following annotations
95 [...]
97 <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/python</annotate>
98 <annotate key="org.freedesktop.policykit.exec.argv1">/usr/bin/my-pk-test</annotate>
99 [...]
100 can be used to select the appropriate polkit action. Be careful to get
102 the latter annotation right, otherwise it will match any pkexec
103 invocation of /usr/bin/python scripts.
104
106 The following variables are set by pkexec. They can be used in
107 authorization rules and messages shown in authentication dialogs:
108 program
110 Fully qualified path to the program to be executed. Example:
111 “/bin/cat”
112 command_line
114 The requested command-line (do not use this for any security
115 checks, it is not secure). Example: “cat /srv/xyz/foobar”
116 user
118 The user name of the user to execute the program as. Example:
119 “davidz”
120 user.gecos
122 The full name of the user to execute the program as. Example:
123 “David Zeuthen”
124 user.display
126 A representation of the user to execute the program as that is
127 suitable for display in an authentication dialog. Is typically set
128 to a combination of the user name and the full name. Example:
129 “David Zeuthen (davidz)”
130
132 Written by David Zeuthen <davidz@redhat.com> with a lot of help from
133 many others.
134
136 Please send bug reports to either the distribution or the polkit-devel
137 mailing list, see the link
138 http://lists.freedesktop.org/mailman/listinfo/polkit-devel on how to
139 subscribe.
140
142 polkit(8), polkitd(8), pkaction(1), pkcheck(1), pkttyagent(1)
143
145 1. she-bang wrapper
146 http://en.wikipedia.org/wiki/Shebang_(Unix)
147polkit May 2009 PKEXEC(1)