mirror of https://github.com/mkerrisk/man-pages
150 lines
4.3 KiB
Groff
150 lines
4.3 KiB
Groff
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" and Copyright (C) 2007, 2012 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's "POSIX Programmer's Guide" (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified Sat Jul 24 19:30:29 1993 by Rik Faith (faith@cs.unc.edu)
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.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
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.\"
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.TH GETENV 3 2015-08-08 "GNU" "Linux Programmer's Manual"
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.SH NAME
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getenv, secure_getenv \- get an environment variable
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.PP
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.BI "char *getenv(const char *" name );
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.PP
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.BI "char *secure_getenv(const char *" name );
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.fi
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.BR secure_getenv ():
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_GNU_SOURCE
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.SH DESCRIPTION
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The
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.BR getenv ()
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function searches the environment list to find the
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environment variable
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.IR name ,
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and returns a pointer to the corresponding
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.I value
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string.
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.PP
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The GNU-specific
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.BR secure_getenv ()
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function is just like
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.BR getenv ()
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except that it returns NULL in cases where "secure execution" is required.
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Secure execution is required if one of the following conditions
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was true when the program run by the calling process was loaded:
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.IP * 3
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the process's effective user ID did not match its real user ID or
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the process's effective group ID did not match its real group ID
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(typically this is the result of executing a set-user-ID or
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set-group-ID program);
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.IP *
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the effective capability bit was set on the executable file; or
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.IP *
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the process has a nonempty permitted capability set.
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.PP
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Secure execution may also be required if triggered
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by some Linux security modules.
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.PP
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The
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.BR secure_getenv ()
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function is intended for use in general-purpose libraries
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to avoid vulnerabilities that could occur if
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set-user-ID or set-group-ID programs accidentally
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trusted the environment.
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.SH RETURN VALUE
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The
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.BR getenv ()
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function returns a pointer to the value in the
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environment, or NULL if there is no match.
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.SH VERSIONS
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.BR secure_getenv ()
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first appeared in glibc 2.17.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lbw25 lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR getenv (),
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.BR secure_getenv ()
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T} Thread safety MT-Safe env
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.TE
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.SH CONFORMING TO
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.BR getenv ():
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POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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.PP
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.BR secure_getenv ()
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is a GNU extension.
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.SH NOTES
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The strings in the environment list are of the form \fIname=value\fP.
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.PP
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As typically implemented,
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.BR getenv ()
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returns a pointer to a string within the environment list.
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The caller must take care not to modify this string,
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since that would change the environment of the process.
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.PP
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The implementation of
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.BR getenv ()
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is not required to be reentrant.
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The string pointed to by the return value of
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.BR getenv ()
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may be statically allocated,
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and can be modified by a subsequent call to
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.BR getenv (),
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.BR putenv (3),
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.BR setenv (3),
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or
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.BR unsetenv (3).
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.PP
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The "secure execution" mode of
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.BR secure_getenv ()
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is controlled by the
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.B AT_SECURE
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flag contained in the auxiliary vector passed from the kernel to user space.
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.SH SEE ALSO
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.BR clearenv (3),
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.BR getauxval (3),
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.BR putenv (3),
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.BR setenv (3),
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.BR unsetenv (3),
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.BR capabilities (7),
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.BR environ (7)
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