|ENVIRON(7)||Linux Programmer's Manual||ENVIRON(7)|
NAME¶environ - user environment
extern char **environ;
DESCRIPTION¶The variable environ points to an array of pointers to strings called the "environment". The last pointer in this array has the value NULL. (This variable must be declared in the user program, but is declared in the header file <unistd.h> if the _GNU_SOURCE feature test macro is defined.) This array of strings is made available to the process by the exec(3) call that started the process. When a child process is created via fork(2), it inherits a copy of its parent's environment.
- The name of the logged-in user (used by some BSD-derived programs).
- The name of the logged-in user (used by some System-V derived programs).
- The name of a locale to use for locale categories when not overridden by LC_ALL or more specific environment variables such as LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, and LC_TIME (see locale(7) for further details of the LC_* environment variables).
- The sequence of directory prefixes that sh(1) and many other programs apply in searching for a file known by an incomplete pathname. The prefixes are separated by ' :'. (Similarly one has CDPATH used by some shells to find the target of a change directory command, MANPATH used by man(1) to find manual pages, and so on)
- The current working directory. Set by some shells.
- The pathname of the user's login shell.
- The terminal type for which output is to be prepared.
- The user's preferred utility to display text files.
- The user's preferred utility to edit text files.
- The variables LANG, LANGUAGE, NLSPATH, LOCPATH, LC_ALL, LC_MESSAGES, and so on influence locale handling; see catopen(3), gettext(3), and locale(7).
- TMPDIR influences the path prefix of names created by tmpnam(3) and other routines, and the temporary directory used by sort(1) and other programs.
- LD_LIBRARY_PATH, LD_PRELOAD, and other LD_* variables influence the behavior of the dynamic loader/linker.
- POSIXLY_CORRECT makes certain programs and library routines follow the prescriptions of POSIX.
- The behavior of malloc(3) is influenced by MALLOC_* variables.
- The variable HOSTALIASES gives the name of a file containing aliases to be used with gethostbyname(3).
- TZ and TZDIR give timezone information used by tzset(3) and through that by functions like ctime(3), localtime(3), mktime(3), strftime(3). See also tzselect(8).
- TERMCAP gives information on how to address a given terminal (or gives the name of a file containing such information).
- COLUMNS and LINES tell applications about the window size, possibly overriding the actual size.
- PRINTER or LPDEST may specify the desired printer to use. See lpr(1).
NOTES¶The prctl(2) PR_SET_MM_ENV_START and PR_SET_MM_ENV_END operations can be used to control the location of the process's environment.
BUGS¶Clearly there is a security risk here. Many a system command has been tricked into mischief by a user who specified unusual values for IFS or LD_LIBRARY_PATH.
SEE ALSO¶bash(1), csh(1), env(1), login(1), printenv(1), sh(1), tcsh(1), execve(2), clearenv(3), exec(3), getenv(3), putenv(3), setenv(3), unsetenv(3), locale(7), ld.so(8), pam_env(8)
COLOPHON¶This page is part of release 4.10 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/.