mirror of https://github.com/mkerrisk/man-pages
1272 lines
35 KiB
Groff
1272 lines
35 KiB
Groff
.\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl)
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.\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com>
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.\" and Copyright Guillem Jover <guillem@hadrons.org>
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.\" and Copyright (C) 2014 Dave Hansen / Intel
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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.\" manual page may be incorrect or out-of-date.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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.\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG
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.\" Modified 27 Jun 02, Michael Kerrisk
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.\" Added PR_SET_DUMPABLE, PR_GET_DUMPABLE,
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.\" PR_SET_KEEPCAPS, PR_GET_KEEPCAPS
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.\" Modified 2006-08-30 Guillem Jover <guillem@hadrons.org>
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.\" Updated Linux versions where the options where introduced.
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.\" Added PR_SET_TIMING, PR_GET_TIMING, PR_SET_NAME, PR_GET_NAME,
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.\" PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU,
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.\" PR_SET_FPEXC, PR_GET_FPEXC
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.\" 2008-04-29 Serge Hallyn, Document PR_CAPBSET_READ and PR_CAPBSET_DROP
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.\" 2008-06-13 Erik Bosman, <ejbosman@cs.vu.nl>
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.\" Document PR_GET_TSC and PR_SET_TSC.
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.\" 2008-06-15 mtk, Document PR_SET_SECCOMP, PR_GET_SECCOMP
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.\" 2009-10-03 Andi Kleen, document PR_MCE_KILL
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.\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM
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.\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and
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.\" PR_TASK_PERF_EVENTS_ENABLE
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.\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2
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.\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS
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.\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and
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.\" PR_GET_TIMERSLACK
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.\" 2013-01-10 Kees Cook, document PR_SET_PTRACER
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.\" 2012-02-04 Michael kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER
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.\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT
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.\"
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.\"
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.TH PRCTL 2 2015-05-07 "Linux" "Linux Programmer's Manual"
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.SH NAME
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prctl \- operations on a process
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.SH SYNOPSIS
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.nf
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.B #include <sys/prctl.h>
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.sp
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.BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 ,
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.BI " unsigned long " arg4 ", unsigned long " arg5 );
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.fi
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.SH DESCRIPTION
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.BR prctl ()
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is called with a first argument describing what to do
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(with values defined in \fI<linux/prctl.h>\fP), and further
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arguments with a significance depending on the first one.
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The first argument can be:
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.TP
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.BR PR_CAPBSET_READ " (since Linux 2.6.25)"
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Return (as the function result) 1 if the capability specified in
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.I arg2
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is in the calling thread's capability bounding set,
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or 0 if it is not.
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(The capability constants are defined in
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.IR <linux/capability.h> .)
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The capability bounding set dictates
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whether the process can receive the capability through a
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file's permitted capability set on a subsequent call to
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.BR execve (2).
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If the capability specified in
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.I arg2
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is not valid, then the call fails with the error
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.BR EINVAL .
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.TP
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.BR PR_CAPBSET_DROP " (since Linux 2.6.25)"
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If the calling thread has the
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.B CAP_SETPCAP
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capability, then drop the capability specified by
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.I arg2
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from the calling thread's capability bounding set.
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Any children of the calling thread will inherit the newly
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reduced bounding set.
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The call fails with the error:
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.B EPERM
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if the calling thread does not have the
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.BR CAP_SETPCAP ;
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.BR EINVAL
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if
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.I arg2
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does not represent a valid capability; or
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.BR EINVAL
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if file capabilities are not enabled in the kernel,
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in which case bounding sets are not supported.
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.TP
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.BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"
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.\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b
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If
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.I arg2
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is nonzero,
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set the "child subreaper" attribute of the calling process;
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if
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.I arg2
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is zero, unset the attribute.
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When a process is marked as a child subreaper,
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all of the children that it creates, and their descendants,
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will be marked as having a subreaper.
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In effect, a subreaper fulfills the role of
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.BR init (1)
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for its descendant processes.
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Upon termination of a process
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that is orphaned (i.e., its immediate parent has already terminated)
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and marked as having a subreaper,
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the nearest still living ancestor subreaper
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will receive a
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.BR SIGCHLD
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signal and be able to
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.BR wait (2)
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on the process to discover its termination status.
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.TP
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.BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"
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Return the "child subreaper" setting of the caller,
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in the location pointed to by
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.IR "(int\ *) arg2" .
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.TP
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.BR PR_SET_DUMPABLE " (since Linux 2.3.20)"
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Set the state of the "dumpable" flag,
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which determines whether core dumps are produced for the calling process
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upon delivery of a signal whose default behavior is to produce a core dump.
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In kernels up to and including 2.6.12,
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.I arg2
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must be either 0
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.RB ( SUID_DUMP_DISABLE ,
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process is not dumpable) or 1
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.RB ( SUID_DUMP_USER ,
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process is dumpable).
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Between kernels 2.6.13 and 2.6.17,
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.\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502
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the value 2 was also permitted,
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which caused any binary which normally would not be dumped
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to be dumped readable by root only;
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for security reasons, this feature has been removed.
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.\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2
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.\" Subject: Fix prctl privilege escalation (CVE-2006-2451)
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.\" From: Marcel Holtmann <marcel () holtmann ! org>
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.\" Date: 2006-07-12 11:12:00
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(See also the description of
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.I /proc/sys/fs/\:suid_dumpable
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in
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.BR proc (5).)
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Normally, this flag is set to 1.
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However, it is reset to the current value contained in the file
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.IR /proc/sys/fs/\:suid_dumpable
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(which by default has the value 0),
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if any of the following attributes of the process
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are changed by the operations listed below:
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.\" See kernel/cred.c::commit_creds() (Linux 3.18 sources)
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.RS
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.IP * 3
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The effective user or group ID is changed.
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.IP *
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The filesystem user or group ID is changed (see
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.BR credentials (7)).
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.IP *
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The process's set of permitted capabilities (see
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.BR capabilities (7))
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is changed such that its new set of capabilities is
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not a subset of its previous set of capabilities.
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.RE
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.IP
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The operations that may trigger changes to the dumpable flag include:
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.\" Look for uses of commit_creds() in the kernel source code
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.RS
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.IP * 3
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execution
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.RB ( execve (2))
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of a set-user-ID or set-group-ID program,
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or a program that has capabilities (see
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.BR capabilities (7));
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.IP *
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.BR capset (2);
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and
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.IP *
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system calls that change process credentials
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.RB ( setuid (2)
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.BR setgid (2),
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.BR setresuid (2),
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.BR setresgid (2),
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.BR setgroups (2),
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and so on).
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.\" Also certain namespace operations;
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.RE
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.IP
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Processes that are not dumpable can not be attached via
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.BR ptrace (2)
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.BR PTRACE_ATTACH .
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.TP
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.BR PR_GET_DUMPABLE " (since Linux 2.3.20)"
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Return (as the function result) the current state of the calling
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process's dumpable flag.
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.\" Since Linux 2.6.13, the dumpable flag can have the value 2,
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.\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable
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.\" flags has a nonzero value. This was fixed in 2.6.14.
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.TP
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.BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
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Set the endian-ness of the calling process to the value given
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in \fIarg2\fP, which should be one of the following:
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.\" Respectively 0, 1, 2
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.BR PR_ENDIAN_BIG ,
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.BR PR_ENDIAN_LITTLE ,
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or
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.B PR_ENDIAN_PPC_LITTLE
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(PowerPC pseudo little endian).
|
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.TP
|
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.BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
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Return the endian-ness of the calling process,
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in the location pointed to by
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.IR "(int\ *) arg2" .
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.TP
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.BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
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Set floating-point emulation control bits to \fIarg2\fP.
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Pass
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.B PR_FPEMU_NOPRINT
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to silently emulate floating-point operation accesses, or
|
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.B PR_FPEMU_SIGFPE
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to not emulate floating-point operations and send
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.B SIGFPE
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instead.
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.TP
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.BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
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Return floating-point emulation control bits,
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in the location pointed to by
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.IR "(int\ *) arg2" .
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.TP
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.BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
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|
Set floating-point exception mode to \fIarg2\fP.
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Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables,
|
|
\fBPR_FP_EXC_DIV\fP for floating-point divide by zero,
|
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\fBPR_FP_EXC_OVF\fP for floating-point overflow,
|
|
\fBPR_FP_EXC_UND\fP for floating-point underflow,
|
|
\fBPR_FP_EXC_RES\fP for floating-point inexact result,
|
|
\fBPR_FP_EXC_INV\fP for floating-point invalid operation,
|
|
\fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled,
|
|
\fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode,
|
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\fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode,
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\fBPR_FP_EXC_PRECISE\fP for precise exception mode.
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.TP
|
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.BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
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Return floating-point exception mode,
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in the location pointed to by
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.IR "(int\ *) arg2" .
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.TP
|
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.BR PR_SET_KEEPCAPS " (since Linux 2.2.18)"
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Set the state of the thread's "keep capabilities" flag,
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which determines whether the threads's permitted
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capability set is cleared when a change is made to the threads's user IDs
|
|
such that the threads's real UID, effective UID, and saved set-user-ID
|
|
all become nonzero when at least one of them previously had the value 0.
|
|
By default, the permitted capability set is cleared when such a change is made;
|
|
setting the "keep capabilities" flag prevents it from being cleared.
|
|
.I arg2
|
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must be either 0 (permitted capabilities are cleared)
|
|
or 1 (permitted capabilities are kept).
|
|
(A thread's
|
|
.I effective
|
|
capability set is always cleared when such a credential change is made,
|
|
regardless of the setting of the "keep capabilities" flag.)
|
|
The "keep capabilities" value will be reset to 0 on subsequent calls to
|
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.BR execve (2).
|
|
.TP
|
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.BR PR_GET_KEEPCAPS " (since Linux 2.2.18)"
|
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Return (as the function result) the current state of the calling threads's
|
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"keep capabilities" flag.
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.TP
|
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.BR PR_SET_NAME " (since Linux 2.6.9)"
|
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Set the name of the calling thread,
|
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using the value in the location pointed to by
|
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.IR "(char\ *) arg2" .
|
|
The name can be up to 16 bytes long,
|
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.\" TASK_COMM_LEN in include/linux/sched.h
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including the terminating null byte.
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(If the length of the string, including the terminating null byte,
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exceeds 16 bytes, the string is silently truncated.)
|
|
This is the same attribute that can be set via
|
|
.BR pthread_setname_np (3)
|
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and retrieved using
|
|
.BR pthread_getname_np (3).
|
|
The attribute is likewise accessible via
|
|
.IR /proc/self/task/[tid]/comm ,
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|
where
|
|
.I tid
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is the name of the calling thread.
|
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.TP
|
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.BR PR_GET_NAME " (since Linux 2.6.11)"
|
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Return the name of the calling thread,
|
|
in the buffer pointed to by
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.IR "(char\ *) arg2" .
|
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The buffer should allow space for up to 16 bytes;
|
|
the returned string will be null-terminated.
|
|
.TP
|
|
.BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"
|
|
Set the calling process's
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.I no_new_privs
|
|
bit to the value in
|
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.IR arg2 .
|
|
With
|
|
.I no_new_privs
|
|
set to 1,
|
|
.BR execve (2)
|
|
promises not to grant privileges to do anything
|
|
that could not have been done without the
|
|
.BR execve (2)
|
|
call (for example,
|
|
rendering the set-user-ID and set-group-ID mode bits,
|
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and file capabilities non-functional).
|
|
Once set, this bit cannot be unset.
|
|
The setting of this bit is inherited by children created by
|
|
.BR fork (2)
|
|
and
|
|
.BR clone (2),
|
|
and preserved across
|
|
.BR execve (2).
|
|
|
|
For more information, see the kernel source file
|
|
.IR Documentation/prctl/no_new_privs.txt .
|
|
.TP
|
|
.BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)"
|
|
Return (as the function result) the value of the
|
|
.I no_new_privs
|
|
bit for the current process.
|
|
A value of 0 indicates the regular
|
|
.BR execve (2)
|
|
behavior.
|
|
A value of 1 indicates
|
|
.BR execve (2)
|
|
will operate in the privilege-restricting mode described above.
|
|
.TP
|
|
.BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"
|
|
Set the parent death signal
|
|
of the calling process to \fIarg2\fP (either a signal value
|
|
in the range 1..maxsig, or 0 to clear).
|
|
This is the signal that the calling process will get when its
|
|
parent dies.
|
|
This value is cleared for the child of a
|
|
.BR fork (2)
|
|
and (since Linux 2.4.36 / 2.6.23)
|
|
when executing a set-user-ID or set-group-ID binary,
|
|
or a binary that has associated capabilities (see
|
|
.BR capabilities (7)).
|
|
This value is preserved across
|
|
.BR execve (2).
|
|
|
|
.IR Warning :
|
|
.\" https://bugzilla.kernel.org/show_bug.cgi?id=43300
|
|
the "parent" in this case is considered to be the
|
|
.I thread
|
|
that created this process.
|
|
In other words, the signal will be sent when that thread terminates
|
|
(via, for example,
|
|
.BR pthread_exit (3)),
|
|
rather than after all of the threads in the parent process terminate.
|
|
.TP
|
|
.BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"
|
|
Return the current value of the parent process death signal,
|
|
in the location pointed to by
|
|
.IR "(int\ *) arg2" .
|
|
.TP
|
|
.BR PR_SET_PTRACER " (since Linux 3.4)"
|
|
.\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb
|
|
.\" commit bf06189e4d14641c0148bea16e9dd24943862215
|
|
This is meaningful only when the Yama LSM is enabled and in mode 1
|
|
("restricted ptrace", visible via
|
|
.IR /proc/sys/kernel/yama/ptrace_scope ).
|
|
When a "ptracer process ID" is passed in \fIarg2\fP,
|
|
the caller is declaring that the ptracer process can
|
|
.BR ptrace (2)
|
|
the calling process as if it were a direct process ancestor.
|
|
Each
|
|
.B PR_SET_PTRACER
|
|
operation replaces the previous "ptracer process ID".
|
|
Employing
|
|
.B PR_SET_PTRACER
|
|
with
|
|
.I arg2
|
|
set to 0 clears the caller's "ptracer process ID".
|
|
If
|
|
.I arg2
|
|
is
|
|
.BR PR_SET_PTRACER_ANY ,
|
|
the ptrace restrictions introduced by Yama are effectively disabled for the
|
|
calling process.
|
|
|
|
For further information, see the kernel source file
|
|
.IR Documentation/security/Yama.txt .
|
|
.TP
|
|
.BR PR_SET_SECCOMP " (since Linux 2.6.23)"
|
|
.\" See http://thread.gmane.org/gmane.linux.kernel/542632
|
|
.\" [PATCH 0 of 2] seccomp updates
|
|
.\" andrea@cpushare.com
|
|
Set the secure computing (seccomp) mode for the calling thread, to limit
|
|
the available system calls.
|
|
The more recent
|
|
.BR seccomp (2)
|
|
system call provides a superset of the functionality of
|
|
.BR PR_SET_SECCOMP .
|
|
|
|
The seccomp mode is selected via
|
|
.IR arg2 .
|
|
(The seccomp constants are defined in
|
|
.IR <linux/seccomp.h> .)
|
|
|
|
With
|
|
.IR arg2
|
|
set to
|
|
.BR SECCOMP_MODE_STRICT ,
|
|
the only system calls that the thread is permitted to make are
|
|
.BR read (2),
|
|
.BR write (2),
|
|
.BR _exit (2)
|
|
(but not
|
|
.BR exit_group (2)),
|
|
and
|
|
.BR sigreturn (2).
|
|
Other system calls result in the delivery of a
|
|
.BR SIGKILL
|
|
signal.
|
|
Strict secure computing mode is useful for number-crunching applications
|
|
that may need to execute untrusted byte code,
|
|
perhaps obtained by reading from a pipe or socket.
|
|
This operation is available only
|
|
if the kernel is configured with
|
|
.B CONFIG_SECCOMP
|
|
enabled.
|
|
|
|
With
|
|
.IR arg2
|
|
set to
|
|
.BR SECCOMP_MODE_FILTER " (since Linux 3.5),"
|
|
the system calls allowed are defined by a pointer
|
|
to a Berkeley Packet Filter passed in
|
|
.IR arg3 .
|
|
This argument is a pointer to
|
|
.IR "struct sock_fprog" ;
|
|
it can be designed to filter
|
|
arbitrary system calls and system call arguments.
|
|
This mode is available only if the kernel is configured with
|
|
.B CONFIG_SECCOMP_FILTER
|
|
enabled.
|
|
|
|
If
|
|
.BR SECCOMP_MODE_FILTER
|
|
filters permit
|
|
.BR fork (2),
|
|
then the seccomp mode is inherited by children created by
|
|
.BR fork (2);
|
|
if
|
|
.BR execve (2)
|
|
is permitted, then the seccomp mode is preserved across
|
|
.BR execve (2).
|
|
If the filters permit
|
|
.BR prctl ()
|
|
calls, then additional filters can be added;
|
|
they are run in order until the first non-allow result is seen.
|
|
|
|
For further information, see the kernel source file
|
|
.IR Documentation/prctl/seccomp_filter.txt .
|
|
.TP
|
|
.BR PR_GET_SECCOMP " (since Linux 2.6.23)"
|
|
Return (as the function result)
|
|
the secure computing mode of the calling thread.
|
|
If the caller is not in secure computing mode, this operation returns 0;
|
|
if the caller is in strict secure computing mode, then the
|
|
.BR prctl ()
|
|
call will cause a
|
|
.B SIGKILL
|
|
signal to be sent to the process.
|
|
If the caller is in filter mode, and this system call is allowed by the
|
|
seccomp filters, it returns 2; otherwise, the process is killed with a
|
|
.BR SIGKILL
|
|
signal.
|
|
This operation is available only
|
|
if the kernel is configured with
|
|
.B CONFIG_SECCOMP
|
|
enabled.
|
|
|
|
Since Linux 3.8, the
|
|
.IR Seccomp
|
|
field of the
|
|
.IR /proc/[pid]/status
|
|
file provides a method of obtaining the same information,
|
|
without the risk that the process is killed; see
|
|
.BR proc (5).
|
|
.TP
|
|
.BR PR_SET_SECUREBITS " (since Linux 2.6.26)"
|
|
Set the "securebits" flags of the calling thread to the value supplied in
|
|
.IR arg2 .
|
|
See
|
|
.BR capabilities (7).
|
|
.TP
|
|
.BR PR_GET_SECUREBITS " (since Linux 2.6.26)"
|
|
Return (as the function result)
|
|
the "securebits" flags of the calling thread.
|
|
See
|
|
.BR capabilities (7).
|
|
.TP
|
|
.BR PR_SET_THP_DISABLE " (since Linux 3.15)"
|
|
.\" commit a0715cc22601e8830ace98366c0c2bd8da52af52
|
|
Set the state of the "THP disable" flag for the calling thread.
|
|
If
|
|
.I arg2
|
|
has a nonzero value, the flag is set, otherwise it is cleared.
|
|
Setting this flag provides a method
|
|
for disabling transparent huge pages
|
|
for jobs where the code cannot be modified, and using a malloc hook with
|
|
.BR madvise (2)
|
|
is not an option (i.e., statically allocated data).
|
|
The setting of the "THP disable" flag is inherited by a child created via
|
|
.BR fork (2)
|
|
and is preserved across
|
|
.BR execve (2).
|
|
.TP
|
|
.BR PR_GET_THP_DISABLE " (since Linux 3.15)"
|
|
Return (via the function result) the current setting of the "THP disable"
|
|
flag for the calling thread:
|
|
either 1, if the flag is set, or 0, if it is not.
|
|
.TP
|
|
.BR PR_GET_TID_ADDRESS " (since Linux 3.5)"
|
|
.\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d
|
|
Retrieve the
|
|
.I clear_child_tid
|
|
address set by
|
|
.BR set_tid_address (2)
|
|
and the
|
|
.BR clone (2)
|
|
.B CLONE_CHILD_CLEARTID
|
|
flag, in the location pointed to by
|
|
.IR "(int\ **)\ arg2" .
|
|
This feature is available only if the kernel is built with the
|
|
.BR CONFIG_CHECKPOINT_RESTORE
|
|
option enabled.
|
|
.TP
|
|
.BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
|
|
.\" See https://lwn.net/Articles/369549/
|
|
.\" commit 6976675d94042fbd446231d1bd8b7de71a980ada
|
|
Set the current timer slack for the calling thread to the nanosecond value
|
|
supplied in
|
|
.IR arg2 .
|
|
If
|
|
.I arg2
|
|
is less than or equal to zero,
|
|
.\" It seems that it's not possible to set the timer slack to zero;
|
|
.\" The minimum value is 1? Seems a little strange.
|
|
reset the current timer slack to the thread's default timer slack value.
|
|
The timer slack is used by the kernel to group timer expirations
|
|
for the calling thread that are close to one another;
|
|
as a consequence, timer expirations for the thread may be
|
|
up to the specified number of nanoseconds late (but will never expire early).
|
|
Grouping timer expirations can help reduce system power consumption
|
|
by minimizing CPU wake-ups.
|
|
|
|
The timer expirations affected by timer slack are those set by
|
|
.BR select (2),
|
|
.BR pselect (2),
|
|
.BR poll (2),
|
|
.BR ppoll (2),
|
|
.BR epoll_wait (2),
|
|
.BR epoll_pwait (2),
|
|
.BR clock_nanosleep (2),
|
|
.BR nanosleep (2),
|
|
and
|
|
.BR futex (2)
|
|
(and thus the library functions implemented via futexes, including
|
|
.\" List obtained by grepping for futex usage in glibc source
|
|
.BR pthread_cond_timedwait (3),
|
|
.BR pthread_mutex_timedlock (3),
|
|
.BR pthread_rwlock_timedrdlock (3),
|
|
.BR pthread_rwlock_timedwrlock (3),
|
|
and
|
|
.BR sem_timedwait (3)).
|
|
|
|
Timer slack is not applied to threads that are scheduled under
|
|
a real-time scheduling policy (see
|
|
.BR sched_setscheduler (2)).
|
|
|
|
Each thread has two associated timer slack values:
|
|
a "default" value, and a "current" value.
|
|
The current value is the one that governs grouping
|
|
of timer expirations.
|
|
When a new thread is created,
|
|
the two timer slack values are made the same as the current value
|
|
of the creating thread.
|
|
Thereafter, a thread can adjust its current timer slack value via
|
|
.BR PR_SET_TIMERSLACK
|
|
(the default value can't be changed).
|
|
The timer slack values of
|
|
.IR init
|
|
(PID 1), the ancestor of all processes,
|
|
are 50,000 nanoseconds (50 microseconds).
|
|
The timer slack values are preserved across
|
|
.BR execve (2).
|
|
.TP
|
|
.BR PR_GET_TIMERSLACK " (since Linux 2.6.28)"
|
|
Return (as the function result)
|
|
the current timer slack value of the calling thread.
|
|
.TP
|
|
.BR PR_SET_TIMING " (since Linux 2.6.0-test4)"
|
|
Set whether to use (normal, traditional) statistical process timing or
|
|
accurate timestamp-based process timing, by passing
|
|
.B PR_TIMING_STATISTICAL
|
|
.\" 0
|
|
or
|
|
.B PR_TIMING_TIMESTAMP
|
|
.\" 1
|
|
to \fIarg2\fP.
|
|
.B PR_TIMING_TIMESTAMP
|
|
is not currently implemented
|
|
(attempting to set this mode will yield the error
|
|
.BR EINVAL ).
|
|
.\" PR_TIMING_TIMESTAMP doesn't do anything in 2.6.26-rc8,
|
|
.\" and looking at the patch history, it appears
|
|
.\" that it never did anything.
|
|
.TP
|
|
.BR PR_GET_TIMING " (since Linux 2.6.0-test4)"
|
|
Return (as the function result) which process timing method is currently
|
|
in use.
|
|
.TP
|
|
.BR PR_TASK_PERF_EVENTS_DISABLE " (since Linux 2.6.31)"
|
|
Disable all performance counters attached to the calling process,
|
|
regardless of whether the counters were created by
|
|
this process or another process.
|
|
Performance counters created by the calling process for other
|
|
processes are unaffected.
|
|
For more information on performance counters, see the Linux kernel source file
|
|
.IR tools/perf/design.txt .
|
|
.IP
|
|
Originally called
|
|
.BR PR_TASK_PERF_COUNTERS_DISABLE ;
|
|
.\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
|
|
renamed (with same numerical value)
|
|
in Linux 2.6.32.
|
|
.TP
|
|
.BR PR_TASK_PERF_EVENTS_ENABLE " (since Linux 2.6.31)"
|
|
The converse of
|
|
.BR PR_TASK_PERF_EVENTS_DISABLE ;
|
|
enable performance counters attached to the calling process.
|
|
.IP
|
|
Originally called
|
|
.BR PR_TASK_PERF_COUNTERS_ENABLE ;
|
|
.\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
|
|
renamed
|
|
.\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6
|
|
in Linux 2.6.32.
|
|
.TP
|
|
.BR PR_SET_TSC " (since Linux 2.6.26, x86 only)"
|
|
Set the state of the flag determining whether the timestamp counter
|
|
can be read by the process.
|
|
Pass
|
|
.B PR_TSC_ENABLE
|
|
to
|
|
.I arg2
|
|
to allow it to be read, or
|
|
.B PR_TSC_SIGSEGV
|
|
to generate a
|
|
.B SIGSEGV
|
|
when the process tries to read the timestamp counter.
|
|
.TP
|
|
.BR PR_GET_TSC " (since Linux 2.6.26, x86 only)"
|
|
Return the state of the flag determining whether the timestamp counter
|
|
can be read,
|
|
in the location pointed to by
|
|
.IR "(int\ *) arg2" .
|
|
.TP
|
|
.B PR_SET_UNALIGN
|
|
(Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
|
|
PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22)
|
|
Set unaligned access control bits to \fIarg2\fP.
|
|
Pass
|
|
\fBPR_UNALIGN_NOPRINT\fP to silently fix up unaligned user accesses,
|
|
or \fBPR_UNALIGN_SIGBUS\fP to generate
|
|
.B SIGBUS
|
|
on unaligned user access.
|
|
.TP
|
|
.B PR_GET_UNALIGN
|
|
(see
|
|
.B PR_SET_UNALIGN
|
|
for information on versions and architectures)
|
|
Return unaligned access control bits, in the location pointed to by
|
|
.IR "(int\ *) arg2" .
|
|
.TP
|
|
.BR PR_MCE_KILL " (since Linux 2.6.32)"
|
|
Set the machine check memory corruption kill policy for the current thread.
|
|
If
|
|
.I arg2
|
|
is
|
|
.BR PR_MCE_KILL_CLEAR ,
|
|
clear the thread memory corruption kill policy and use the system-wide default.
|
|
(The system-wide default is defined by
|
|
.IR /proc/sys/vm/memory_failure_early_kill ;
|
|
see
|
|
.BR proc (5).)
|
|
If
|
|
.I arg2
|
|
is
|
|
.BR PR_MCE_KILL_SET ,
|
|
use a thread-specific memory corruption kill policy.
|
|
In this case,
|
|
.I arg3
|
|
defines whether the policy is
|
|
.I early kill
|
|
.RB ( PR_MCE_KILL_EARLY ),
|
|
.I late kill
|
|
.RB ( PR_MCE_KILL_LATE ),
|
|
or the system-wide default
|
|
.RB ( PR_MCE_KILL_DEFAULT ).
|
|
Early kill means that the thread receives a
|
|
.B SIGBUS
|
|
signal as soon as hardware memory corruption is detected inside
|
|
its address space.
|
|
In late kill mode, the process is killed only when it accesses a corrupted page.
|
|
See
|
|
.BR sigaction (2)
|
|
for more information on the
|
|
.BR SIGBUS
|
|
signal.
|
|
The policy is inherited by children.
|
|
The remaining unused
|
|
.BR prctl ()
|
|
arguments must be zero for future compatibility.
|
|
.TP
|
|
.BR PR_MCE_KILL_GET " (since Linux 2.6.32)"
|
|
Return the current per-process machine check kill policy.
|
|
All unused
|
|
.BR prctl ()
|
|
arguments must be zero.
|
|
.TP
|
|
.BR PR_SET_MM " (since Linux 3.3)"
|
|
.\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036
|
|
Modify certain kernel memory map descriptor fields
|
|
of the calling process.
|
|
Usually these fields are set by the kernel and dynamic loader (see
|
|
.BR ld.so (8)
|
|
for more information) and a regular application should not use this feature.
|
|
However, there are cases, such as self-modifying programs,
|
|
where a program might find it useful to change its own memory map.
|
|
This feature is available only if the kernel is built with the
|
|
.BR CONFIG_CHECKPOINT_RESTORE
|
|
option enabled.
|
|
The calling process must have the
|
|
.BR CAP_SYS_RESOURCE
|
|
capability.
|
|
The value in
|
|
.I arg2
|
|
is one of the options below, while
|
|
.I arg3
|
|
provides a new value for the option.
|
|
.RS
|
|
.TP
|
|
.BR PR_SET_MM_START_CODE
|
|
Set the address above which the program text can run.
|
|
The corresponding memory area must be readable and executable,
|
|
but not writable or sharable (see
|
|
.BR mprotect (2)
|
|
and
|
|
.BR mmap (2)
|
|
for more information).
|
|
.TP
|
|
.BR PR_SET_MM_END_CODE
|
|
Set the address below which the program text can run.
|
|
The corresponding memory area must be readable and executable,
|
|
but not writable or sharable.
|
|
.TP
|
|
.BR PR_SET_MM_START_DATA
|
|
Set the address above which initialized and
|
|
uninitialized (bss) data are placed.
|
|
The corresponding memory area must be readable and writable,
|
|
but not executable or sharable.
|
|
.TP
|
|
.B PR_SET_MM_END_DATA
|
|
Set the address below which initialized and
|
|
uninitialized (bss) data are placed.
|
|
The corresponding memory area must be readable and writable,
|
|
but not executable or sharable.
|
|
.TP
|
|
.BR PR_SET_MM_START_STACK
|
|
Set the start address of the stack.
|
|
The corresponding memory area must be readable and writable.
|
|
.TP
|
|
.BR PR_SET_MM_START_BRK
|
|
Set the address above which the program heap can be expanded with
|
|
.BR brk (2)
|
|
call.
|
|
The address must be greater than the ending address of
|
|
the current program data segment.
|
|
In addition, the combined size of the resulting heap and
|
|
the size of the data segment can't exceed the
|
|
.BR RLIMIT_DATA
|
|
resource limit (see
|
|
.BR setrlimit (2)).
|
|
.TP
|
|
.BR PR_SET_MM_BRK
|
|
Set the current
|
|
.BR brk (2)
|
|
value.
|
|
The requirements for the address are the same as for the
|
|
.BR PR_SET_MM_START_BRK
|
|
option.
|
|
.P
|
|
The following options are available since Linux 3.5.
|
|
.\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7
|
|
.TP
|
|
.BR PR_SET_MM_ARG_START
|
|
Set the address above which the program command line is placed.
|
|
.TP
|
|
.BR PR_SET_MM_ARG_END
|
|
Set the address below which the program command line is placed.
|
|
.TP
|
|
.BR PR_SET_MM_ENV_START
|
|
Set the address above which the program environment is placed.
|
|
.TP
|
|
.BR PR_SET_MM_ENV_END
|
|
Set the address below which the program environment is placed.
|
|
.IP
|
|
The address passed with
|
|
.BR PR_SET_MM_ARG_START ,
|
|
.BR PR_SET_MM_ARG_END ,
|
|
.BR PR_SET_MM_ENV_START ,
|
|
and
|
|
.BR PR_SET_MM_ENV_END
|
|
should belong to a process stack area.
|
|
Thus, the corresponding memory area must be readable, writable, and
|
|
(depending on the kernel configuration) have the
|
|
.BR MAP_GROWSDOWN
|
|
attribute set (see
|
|
.BR mmap (2)).
|
|
.TP
|
|
.BR PR_SET_MM_AUXV
|
|
Set a new auxiliary vector.
|
|
The
|
|
.I arg3
|
|
argument should provide the address of the vector.
|
|
The
|
|
.I arg4
|
|
is the size of the vector.
|
|
.TP
|
|
.BR PR_SET_MM_EXE_FILE
|
|
.\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6
|
|
Supersede the
|
|
.IR /proc/pid/exe
|
|
symbolic link with a new one pointing to a new executable file
|
|
identified by the file descriptor provided in
|
|
.I arg3
|
|
argument.
|
|
The file descriptor should be obtained with a regular
|
|
.BR open (2)
|
|
call.
|
|
.IP
|
|
To change the symbolic link, one needs to unmap all existing
|
|
executable memory areas, including those created by the kernel itself
|
|
(for example the kernel usually creates at least one executable
|
|
memory area for the ELF
|
|
.IR \.text
|
|
section).
|
|
.IP
|
|
The second limitation is that such transitions can be done only once
|
|
in a process life time.
|
|
Any further attempts will be rejected.
|
|
This should help system administrators monitor unusual
|
|
symbolic-link transitions over all processes running on a system.
|
|
.RE
|
|
.TP
|
|
.BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "
|
|
.\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c
|
|
.\" See also http://lwn.net/Articles/582712/
|
|
.\" See also https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler
|
|
Enable or disable kernel management of Memory Protection eXtensions (MPX)
|
|
bounds tables.
|
|
The
|
|
.IR arg2 ,
|
|
.IR arg3 ,
|
|
.IR arg4 ,
|
|
and
|
|
.IR arg5
|
|
.\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88
|
|
arguments must be zero.
|
|
|
|
MPX is a hardware-assisted mechanism for performing bounds checking on
|
|
pointers.
|
|
It consists of a set of registers storing bounds information
|
|
and a set of special instruction prefixes that tell the CPU on which
|
|
instructions it should do bounds enforcement.
|
|
There is a limited number of these registers and
|
|
when there are more pointers than registers,
|
|
their contents must be "spilled" into a set of tables.
|
|
These tables are called "bounds tables" and the MPX
|
|
.BR prctl ()
|
|
operations control
|
|
whether the kernel manages their allocation and freeing.
|
|
|
|
When management is enabled, the kernel will take over allocation
|
|
and freeing of the bounds tables.
|
|
It does this by trapping the #BR exceptions that result
|
|
at first use of missing bounds tables and
|
|
instead of delivering the exception to user space,
|
|
it allocates the table and populates the bounds directory
|
|
with the location of the new table.
|
|
For freeing, the kernel checks to see if bounds tables are
|
|
present for memory which is not allocated, and frees them if so.
|
|
|
|
Before enabling MPX management using
|
|
.BR PR_MPX_ENABLE_MANAGEMENT ,
|
|
the application must first have allocated a user-space buffer for
|
|
the bounds directory and placed the location of that directory in the
|
|
.I bndcfgu
|
|
register.
|
|
|
|
These calls will fail if the CPU or kernel does not support MPX.
|
|
Kernel support for MPX is enabled via the
|
|
.BR CONFIG_X86_INTEL_MPX
|
|
configuration option.
|
|
You can check whether the CPU supports MPX by looking for the 'mpx'
|
|
CPUID bit, like with the following command:
|
|
|
|
cat /proc/cpuinfo | grep ' mpx '
|
|
|
|
A thread may not switch in or out of long (64-bit) mode while MPX is
|
|
enabled.
|
|
|
|
All threads in a process are affected by these calls.
|
|
|
|
The child of a
|
|
.BR fork (2)
|
|
inherits the state of MPX management.
|
|
During
|
|
.BR execve (2),
|
|
MPX management is reset to a state as if
|
|
.BR PR_MPX_DISABLE_MANAGEMENT
|
|
had been called.
|
|
|
|
For further information on Intel MPX, see the kernel source file
|
|
.IR Documentation/x86/intel_mpx.txt .
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.\"
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.SH RETURN VALUE
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On success,
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.BR PR_GET_DUMPABLE ,
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.BR PR_GET_KEEPCAPS ,
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.BR PR_GET_NO_NEW_PRIVS ,
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.BR PR_GET_THP_DISABLE ,
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.BR PR_CAPBSET_READ ,
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.BR PR_GET_TIMING ,
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.BR PR_GET_TIMERSLACK ,
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.BR PR_GET_SECUREBITS ,
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.BR PR_MCE_KILL_GET ,
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and (if it returns)
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.BR PR_GET_SECCOMP
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return the nonnegative values described above.
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All other
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.I option
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values return 0 on success.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EFAULT
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.I arg2
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is an invalid address.
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.TP
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.B EFAULT
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.I option
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is
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.BR PR_SET_SECCOMP ,
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.I arg2
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is
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.BR SECCOMP_MODE_FILTER ,
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the system was built with
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.BR CONFIG_SECCOMP_FILTER ,
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and
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.I arg3
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is an invalid address.
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.TP
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.B EINVAL
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The value of
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.I option
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is not recognized.
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_MCE_KILL
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or
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.BR PR_MCE_KILL_GET
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or
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.BR PR_SET_MM ,
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and unused
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.BR prctl ()
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arguments were not specified as zero.
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.TP
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.B EINVAL
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.I arg2
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is not valid value for this
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.IR option .
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_SECCOMP
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or
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.BR PR_GET_SECCOMP ,
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and the kernel was not configured with
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.BR CONFIG_SECCOMP .
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_SECCOMP ,
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.I arg2
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is
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.BR SECCOMP_MODE_FILTER ,
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and the kernel was not configured with
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.BR CONFIG_SECCOMP_FILTER .
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_MM ,
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and one of the following is true
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.RS
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.IP * 3
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.I arg4
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or
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.I arg5
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is nonzero;
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.IP *
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.I arg3
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is greater than
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.B TASK_SIZE
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(the limit on the size of the user address space for this architecture);
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.IP *
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.I arg2
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is
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.BR PR_SET_MM_START_CODE ,
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.BR PR_SET_MM_END_CODE ,
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.BR PR_SET_MM_START_DATA ,
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.BR PR_SET_MM_END_DATA ,
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or
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.BR PR_SET_MM_START_STACK ,
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and the permissions of the corresponding memory area are not as required;
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.IP *
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.I arg2
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is
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.BR PR_SET_MM_START_BRK
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or
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.BR PR_SET_MM_BRK ,
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and
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.I arg3
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is less than or equal to the end of the data segment
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or specifies a value that would cause the
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.B RLIMIT_DATA
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resource limit to be exceeded.
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.RE
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_PTRACER
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and
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.I arg2
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is not 0,
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.BR PR_SET_PTRACER_ANY ,
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or the PID of an existing process.
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.TP
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.B EINVAL
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.I option
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is
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.B PR_SET_PDEATHSIG
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and
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.I arg2
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is not a valid signal number.
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_DUMPABLE
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and
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.I arg2
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is neither
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.B SUID_DUMP_DISABLE
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nor
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.BR SUID_DUMP_USER .
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_TIMING
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and
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.I arg2
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is not
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.BR PR_TIMING_STATISTICAL .
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_NO_NEW_PRIVS
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and
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.I arg2
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is not equal to 1
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or
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.IR arg3 ,
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.IR arg4 ,
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or
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.IR arg5
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is nonzero.
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_GET_NO_NEW_PRIVS
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and
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.IR arg2 ,
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.IR arg3 ,
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.IR arg4 ,
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or
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.IR arg5
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is nonzero.
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_THP_DISABLE
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and
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.IR arg3 ,
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.IR arg4 ,
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or
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.IR arg5
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is nonzero.
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_GET_THP_DISABLE
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and
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.IR arg2 ,
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.IR arg3 ,
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.IR arg4 ,
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or
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.IR arg5
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is nonzero.
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.TP
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.B EPERM
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.I option
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is
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.BR PR_SET_SECUREBITS ,
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and the caller does not have the
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.B CAP_SETPCAP
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capability,
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or tried to unset a "locked" flag,
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or tried to set a flag whose corresponding locked flag was set
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(see
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.BR capabilities (7)).
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.TP
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.B EPERM
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.I option
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is
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.BR PR_SET_KEEPCAPS ,
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and the callers's
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.B SECURE_KEEP_CAPS_LOCKED
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flag is set
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(see
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.BR capabilities (7)).
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.TP
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.B EPERM
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.I option
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is
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.BR PR_CAPBSET_DROP ,
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and the caller does not have the
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.B CAP_SETPCAP
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capability.
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.TP
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.B EPERM
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.I option
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is
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.BR PR_SET_MM ,
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and the caller does not have the
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.B CAP_SYS_RESOURCE
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capability.
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.TP
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.B EACCES
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.I option
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is
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.BR PR_SET_MM ,
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and
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.I arg3
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is
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.BR PR_SET_MM_EXE_FILE ,
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the file is not executable.
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.TP
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.B EBUSY
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.I option
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is
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.BR PR_SET_MM ,
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.I arg3
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is
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.BR PR_SET_MM_EXE_FILE ,
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and this the second attempt to change the
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.I /proc/pid/exe
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symbolic link, which is prohibited.
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.TP
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.B EBADF
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.I option
|
|
is
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|
.BR PR_SET_MM ,
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|
.I arg3
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is
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|
.BR PR_SET_MM_EXE_FILE ,
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and the file descriptor passed in
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.I arg4
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is not valid.
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.\" The following can't actually happen, because prctl() in
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.\" seccomp mode will cause SIGKILL.
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.\" .TP
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.\" .B EPERM
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.\" .I option
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.\" is
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.\" .BR PR_SET_SECCOMP ,
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.\" and secure computing mode is already 1.
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.TP
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.B ENXIO
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.I option
|
|
was
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.BR PR_MPX_ENABLE_MANAGEMENT
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or
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.BR PR_MPX_DISABLE_MANAGEMENT
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and the kernel or the CPU does not support MPX management.
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Check that the kernel and processor have MPX support.
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.SH VERSIONS
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The
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.BR prctl ()
|
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system call was introduced in Linux 2.1.57.
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.\" The library interface was added in glibc 2.0.6
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.SH CONFORMING TO
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This call is Linux-specific.
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IRIX has a
|
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.BR prctl ()
|
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system call (also introduced in Linux 2.1.44
|
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as irix_prctl on the MIPS architecture),
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with prototype
|
|
.sp
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.BI "ptrdiff_t prctl(int " option ", int " arg2 ", int " arg3 );
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.sp
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and options to get the maximum number of processes per user,
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get the maximum number of processors the calling process can use,
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find out whether a specified process is currently blocked,
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get or set the maximum stack size, and so on.
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.SH SEE ALSO
|
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.BR signal (2),
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.BR core (5)
|