memusage.1, memusagestat.1, pldd.1, accept.2, adjtimex.2, arch_prctl.2, bdflush.2...

[thirdparty/man-pages.git] / man2 / setuid.2

diff --git a/man2/setuid.2 b/man2/setuid.2
index 7df9d27aea96a97a6a80b10d36fc48a4f147ac3b..d32a63ba10455af79695762f22eed1d3aa0edb65 100644 (file)
--- a/man2/setuid.2
+++ b/man2/setuid.2
@@ -1,4 +1,5 @@
 .\" Copyright (C), 1994, Graeme W. Wilford (Wilf).
+.\" and Copyright (C) 2010, 2014, 2015, Michael Kerrisk <mtk.manpages@gmail.com>
 .\"
 .\" %%%LICENSE_START(VERBATIM)
 .\" Permission is granted to make and distribute verbatim copies of this
@@ -27,7 +28,7 @@
 .\"   <richard@greenend.org.uk>, aeb 970616.
 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
 .\"     Added notes on capability requirements
-.TH SETUID 2 2010-11-22 "Linux" "Linux Programmer's Manual"
+.TH SETUID 2 2016-10-08 "Linux" "Linux Programmer's Manual"
 .SH NAME
 setuid \- set user identity
 .SH SYNOPSIS
@@ -39,7 +40,10 @@ setuid \- set user identity
 .SH DESCRIPTION
 .BR setuid ()
 sets the effective user ID of the calling process.
-If the effective UID of the caller is root,
+If the calling process is privileged
+(more precisely: if the process has the
+.BR CAP_SETUID
+capability in its user namespace),
 the real UID and saved set-user-ID are also set.
 .PP
 Under Linux,
@@ -103,6 +107,11 @@ see the description of
 in
 .BR execve (2).
 .TP
+.B EINVAL
+The user ID specified in
+.I uid
+is not valid in this user namespace.
+.TP
 .B EPERM
 The user is not privileged (Linux: does not have the
 .B CAP_SETUID
@@ -110,7 +119,7 @@ capability) and
 .I uid
 does not match the real UID or saved set-user-ID of the calling process.
 .SH CONFORMING TO
-SVr4, POSIX.1-2001.
+POSIX.1-2001, POSIX.1-2008, SVr4.
 Not quite compatible with the 4.4BSD call, which
 sets all of the real, saved, and effective user IDs.
 .\" SVr4 documents an additional EINVAL error condition.
@@ -137,10 +146,26 @@ supporting 32-bit IDs.
 The glibc
 .BR setuid ()
 wrapper function transparently deals with the variation across kernel versions.
+.\"
+.SS C library/kernel differences
+At the kernel level, user IDs and group IDs are a per-thread attribute.
+However, POSIX requires that all threads in a process
+share the same credentials.
+The NPTL threading implementation handles the POSIX requirements by
+providing wrapper functions for
+the various system calls that change process UIDs and GIDs.
+These wrapper functions (including the one for
+.BR setuid ())
+employ a signal-based technique to ensure
+that when one thread changes credentials,
+all of the other threads in the process also change their credentials.
+For details, see
+.BR nptl (7).
 .SH SEE ALSO
 .BR getuid (2),
 .BR seteuid (2),
 .BR setfsuid (2),
 .BR setreuid (2),
 .BR capabilities (7),
-.BR credentials (7)
+.BR credentials (7),
+.BR user_namespaces (7)