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25 .TH FEXECVE 3 2017-09-15 "Linux" "Linux Programmer's Manual"
27 fexecve \- execute program specified via file descriptor
30 .B #include <unistd.h>
32 .BI "int fexecve(int " fd ", char *const " argv "[], char *const " envp []);
36 Feature Test Macro Requirements for glibc (see
37 .BR feature_test_macros (7)):
46 _POSIX_C_SOURCE\ >=\ 200809L
55 performs the same task as
57 with the difference that the file to be executed
58 is specified via a file descriptor,
60 rather than via a pathname.
63 must be opened read-only
68 and the caller must have permission to execute the file that it refers to.
73 On error, the function does return, with a result value of \-1, and
79 with the following additions:
83 is not a valid file descriptor, or
92 filesystem could not be accessed.
95 is implemented since glibc 2.3.2.
97 For an explanation of the terms used in this section, see
103 Interface Attribute Value
106 T} Thread safety MT-Safe
111 This function is not specified in POSIX.1-2001,
112 and is not widely available on other systems.
113 It is specified in POSIX.1-2008.
115 On Linux with glibc versions 2.26 and earlier,
117 is implemented using the
121 needs to be mounted and available at the time of the call.
123 .\" glibc commit 43ffc53a352a67672210c9dd4959f6c6b7407e60
124 if the underlying kernel supports the
128 is implemented using that system call, with the benefit that
130 does not need to be mounted.
134 is to allow the caller to verify (checksum) the contents of
135 an executable before executing it.
136 Simply opening the file, checksumming the contents, and then doing an
138 would not suffice, since, between the two steps, the filename,
139 or a directory prefix of the pathname, could have been exchanged
140 (by, for example, modifying the target of a symbolic link).
142 does not mitigate the problem that the
144 of a file could be changed between the checksumming and the call to
146 for that, the solution is to ensure that the permissions on the file
147 prevent it from being modified by malicious users.
149 The natural idiom when using
151 is to set the close-on-exec flag on
153 so that the file descriptor does not leak through to the program
155 This approach is natural for two reasons.
156 First, it prevents file descriptors being consumed unnecessarily.
157 (The executed program normally has no need of a file descriptor
158 that refers to the program itself.)
162 employing the close-on-exec flag prevents the file descriptor exhaustion
163 that would result from the fact that each step in the recursion would
164 cause one more file descriptor to be passed to the new program.
169 refers to a script (i.e., it is an executable text file that names
170 a script interpreter with a first line that begins with the characters
172 and the close-on-exec flag has been set for
178 This error occurs because,
179 by the time the script interpreter is executed,
181 has already been closed because of the close-on-exec flag.
182 Thus, the close-on-exec flag can't be set on
184 if it refers to a script, leading to the problems described in NOTES.