getenv, secure_getenv - get an environment variable
char *getenv(const char *name);
char *secure_getenv(const char *name);
Feature Test Macro Requirements for glibc (see feature_test_macros
() function searches the environment list to find the
environment variable name
, and returns a pointer to the corresponding
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
- 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
() 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.
() function returns a pointer to the value in the environment,
or NULL if there is no match.
() first appeared in glibc 2.17.
For an explanation of the terms used in this section, see attributes
|getenv (), secure_getenv ()
(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
() is a GNU extension.
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
(3), or unsetenv
The "secure execution" mode of secure_getenv
() is controlled by
flag contained in the auxiliary vector passed from the
kernel to user space.