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Add text describing limit on total size of argv + evnp, 

and changes that occurred with 2.6.23.
Add getopt(3) to SEE ALSO list.
This commit is contained in:
Michael Kerrisk 2007-09-10 04:31:59 +00:00
parent d9a0b2a566
commit d739f5f8c7
1 changed files with 43 additions and 1 deletions
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44
man2/execve.2
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@ -31,8 +31,10 @@
.\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
.\" 2006-09-04 Michael Kerrisk <mtk-manpages@gmx.net>
.\" Added list of process attributes that are not preserved on exec().
.\" 2007-09-14 Ollie Wild <aaw@google.com>, mtk
.\" Add text describing limits on command-line arguments + environment
.\"
.TH EXECVE 2 2006-09-04 "Linux" "Linux Programmer's Manual"
.TH EXECVE 2 2007-09-14 "Linux" "Linux Programmer's Manual"
.SH NAME
execve \- execute program
.SH SYNOPSIS
@ -276,6 +278,45 @@ For portable use,
.I optional-arg
should either be absent, or be specified as a single word (i.e., it
should not contain white space); see NOTES below.
.SS "Limits on size of arguments + environment"
Most Unix implementations impose some limit on the total size
of the command-line argument
.RI ( argv )
and environment
.RI ( envp )
strings that may be passed to a new program.
POSIX.1 allows an implementation to advertise this limit using the
.BR ARG_MAX
constant (either defined in
.I <limits.h>
or available at run time using the call
.IR "sysconf(_SC_ARG_MAX)" ).
On Linux prior to kernel 2.6.23, the memory used to store the
environment and argument strings was limited to 32 pages
(defined by the kernel constant
.BR MAX_ARG_PAGES ).
On architectures with a 4-kB page size,
this yields a maximum size of 128 kB.
On kernel 2.6.23 and later, most architectures support a size limit
derived from the soft
.B RLIMIT_STACK
resource limit (see
.BR getrlimit (2)).
For
these architectures, the total size is limited to 1/4 of the allowed
stack size, the limit per string is 32 pages (the kernel constant
.BR MAX_ARG_STRLEN),
and the maximum number of strings is 0x7FFFFFFF.
(This change allows programs to have a much larger
argument and/or environment list.
Imposing the 1/4-limit
ensures that the new program always has some stack space.)
Architectures with no memory management unit are excepted:
they maintain the pre-2.6.23 limit.
.\" Ollie: That doesn't include the lists of pointers, though,
.\" so the actual usage is a bit higher (1 pointer per argument).
.SH "RETURN VALUE"
On success,
.BR execve ()
@ -552,6 +593,7 @@ argv[4]: world
.BR ptrace (2),
.BR execl (3),
.BR fexecve (3),
.BR getopt (3),
.BR environ (7),
.BR credentials (7),
.BR path_resolution (7),