GETENV
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
getenv, secure_getenv - get an environment variable
SYNOPSIS
#include <stdlib.h>
char *getenv(const char *name);
char *secure_getenv(const char *name);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
secure_getenv():
_GNU_SOURCE
DESCRIPTION
The
getenv()
function searches the environment list to find the
environment variable
name,
and returns a pointer to the corresponding
value
string.
The GNU-specific
secure_getenv()
function is just like
getenv()
except that it returns NULL in cases where "secure execution" is required.
Secure execution is required if one of the following conditions
was true when the program run by the calling process was loaded:
- *
-
the process's effective user ID did not match its real user ID or
the process's effective group ID did not match its real group ID
(typically this is the result of executing a set-user-ID or
set-group-ID program);
- *
-
the effective capability bit was set on the executable file; or
- *
-
the process has a nonempty permitted capability set.
Secure execution may also be required if triggered
by some Linux security modules.
The
secure_getenv()
function is intended for use in general-purpose libraries
to avoid vulnerabilities that could occur if
set-user-ID or set-group-ID programs accidentally
trusted the environment.
RETURN VALUE
The
getenv()
function returns a pointer to the value in the
environment, or NULL if there is no match.
VERSIONS
secure_getenv()
first appeared in glibc 2.17.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
getenv(),
secure_getenv()
| Thread safety | MT-Safe env
|
CONFORMING TO
getenv():
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
secure_getenv()
is a GNU extension.
NOTES
The strings in the environment list are of the form
name=value.
As typically implemented,
getenv()
returns a pointer to a string within the environment list.
The caller must take care not to modify this string,
since that would change the environment of the process.
The implementation of
getenv()
is not required to be reentrant.
The string pointed to by the return value of
getenv()
may be statically allocated,
and can be modified by a subsequent call to
getenv(),
putenv(3),
setenv(3),
or
unsetenv(3).
The "secure execution" mode of
secure_getenv()
is controlled by the
AT_SECURE
flag contained in the auxiliary vector passed from the kernel to user space.
SEE ALSO
clearenv(3),
getauxval(3),
putenv(3),
setenv(3),
unsetenv(3),
capabilities(7),
environ(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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- Running on 
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