1PKEXEC(1) pkexec PKEXEC(1)
2
6 pkexec - Execute a command as another user
7
9 pkexec [--version] [--disable-internal-agent] [--help]
10 pkexec [--keep-cwd] [--user username] PROGRAM [ARGUMENTS...]
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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.
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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 pkexec will run PROGRAM in username's home directory, unless --keep-cwd
54 is used to override this behavior
55 Note that pkexec does no validation of the ARGUMENTS passed to PROGRAM.
57 In the normal case (where administrator authentication is required
58 every time pkexec is used), this is not a problem since if the user is
59 an administrator he might as well just run pkexec bash to get root.
60 However, if an action is used for which the user can retain
62 authorization (or if the user is implicitly authorized) this could be a
63 security hole. Therefore, as a rule of thumb, programs for which the
64 default required authorization is changed, should never implicitly
65 trust user input (e.g. like any other well-written suid program).
66
68 By default, the org.freedesktop.policykit.exec action is used. To use
69 another action, use the org.freedesktop.policykit.exec.path annotation
70 on an action with the value set to the full path of the program. In
71 addition to specifying the program, the authentication message,
72 description, icon and defaults can be specified. If the
73 org.freedesktop.policykit.exec.argv1 annotation is present, the action
74 will only be picked if the first argument to the program matches the
75 value of the annotation.
76 Note that authentication messages may reference variables (see the
78 section called “VARIABLES”), for example $(user) will be expanded to
79 the value of the user variable.
80
82 To avoid modifying existing software to prefix their command-line
83 invocations with pkexec, it's possible to use pkexec in a she-bang
84 wrapper[1] like this:
85 #!/usr/bin/pkexec /usr/bin/python
87 import os
89 import sys
90 print "Hello, I'm running as uid %d"%(os.getuid())
92 for n in range(len(sys.argv)):
94 print "arg[%d]=`%s'"%(n, sys.argv[n])
95 If this script is installed into /usr/bin/my-pk-test, then the
97 following annotations
98 [...]
100 <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/python</annotate>
101 <annotate key="org.freedesktop.policykit.exec.argv1">/usr/bin/my-pk-test</annotate>
102 [...]
103 can be used to select the appropriate polkit action. Be careful to get
105 the latter annotation right, otherwise it will match any pkexec
106 invocation of /usr/bin/python scripts.
107
109 The following variables are set by pkexec. They can be used in
110 authorization rules and messages shown in authentication dialogs:
111 program
113 Fully qualified path to the program to be executed. Example:
114 “/bin/cat”
115 command_line
117 The requested command-line (do not use this for any security
118 checks, it is not secure). Example: “cat /srv/xyz/foobar”
119 user
121 The user name of the user to execute the program as. Example:
122 “davidz”
123 user.gecos
125 The full name of the user to execute the program as. Example:
126 “David Zeuthen”
127 user.display
129 A representation of the user to execute the program as that is
130 suitable for display in an authentication dialog. Is typically set
131 to a combination of the user name and the full name. Example:
132 “David Zeuthen (davidz)”
133
135 Written by David Zeuthen <davidz@redhat.com> with a lot of help from
136 many others.
137
139 Please send bug reports to either the distribution or the polkit-devel
140 mailing list, see the link
141 http://lists.freedesktop.org/mailman/listinfo/polkit-devel on how to
142 subscribe.
143
145 polkit(8), polkitd(8), pkaction(1), pkcheck(1), pkttyagent(1)
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148 1. she-bang wrapper
149 http://en.wikipedia.org/wiki/Shebang_(Unix)
150polkit May 2009 PKEXEC(1)