Open Source Software

getenv(3)



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 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 4.09 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/.



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