man-pages/man2/prctl.2

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.\" the source, must acknowledge the copyright and authors of this work.
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.\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG
.\" Modified 27 Jun 02, Michael Kerrisk
.\" 	Added PR_SET_DUMPABLE, PR_GET_DUMPABLE, 
.\"	PR_SET_KEEPCAPS, PR_GET_KEEPCAPS
.\"
.\" FIXME The following (applicable only on IA-64) are not currently
.\" described: PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU
.\"
.TH PRCTL 2 2002-06-27 "Linux 2.4.18" "Linux Programmer's Manual"
.SH NAME
prctl \- operations on a process
.SH SYNOPSIS
.B #include <sys/prctl.h>
.sp
.BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3
.BI ", unsigned long " arg4 ", unsigned long " arg5 );
.SH DESCRIPTION
.BR prctl ()
is called with a first argument describing what to do
(with values defined in <\fIlinux/prctl.h\fP>), and further
parameters with a significance depending on the first one.
The first argument can be:
.TP
.B PR_SET_PDEATHSIG
(since Linux 2.1.57)
Set the parent process death signal
of the current process to \fIarg2\fP (either a signal value
in the range 1..maxsig, or 0 to clear).
This is the signal that the current process will get when its
parent dies. 
This value is cleared upon a 
.BR fork ().
.TP
.B PR_GET_PDEATHSIG
(since Linux 2.3.15)
Read the current value of the parent process death signal
into the (int *) \fIarg2\fP.
.TP
.B PR_SET_DUMPABLE
(Since Linux 2.4)
Set the state of the flag determining whether core dumps are produced
for this process upon delivery of a signal whose default behaviour is
to produce a core dump.
(Normally this flag is set for a process by default, but it is cleared
when a set-user-ID or set-group-ID program is executed and also by 
various system calls that manipulate process UIDs and GIDs).
In kernels up to and including 2.6.12,
.I arg2
must be either 0 (process is not dumpable) or 1 (process is dumpable).
Since kernel 2.6.13, the value 2 is also permitted;
this causes any binary which normally would not be dumped 
to be dumped readable by root only. 
(See also the description of 
.I /proc/sys/fs/suid_dumpable
in
.BR proc (5).)
.TP
.B PR_GET_DUMPABLE
(Since Linux 2.4)
Return (as the function result) the current state of the calling
process's dumpable flag.
.\" Since Linux 2.6.13, the dumpable flag can have the value 2, 
.\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable
.\" flags has a non-zero value.  This was fixed in 2.6.14.
.TP
.B PR_SET_KEEPCAPS
Set the state of the process's "keep capabilities" flag,
which determines whether the process's effective and permitted
capability sets are cleared when a change is made to the process's user IDs
such that the process's real UID, effective UID, and saved set-user-ID
all become non-zero when at least one of them previously had the value 0.
(By default, these credential sets are cleared).
.I arg2
must be either 0 (capabilities are cleared) or 1 (capabilities are kept).
.TP
.B PR_GET_KEEPCAPS
Return (as the function result) the current state of the calling process's
"keep capabilities" flag.
.SH "RETURN VALUE"
.B PR_GET_DUMPABLE
and
.B PR_GET_KEEPCAPS
return 0 or 1 on success.
All other
.I option
values return 0 on success.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
The value of
.I option
is not recognized, or it is
.B PR_SET_PDEATHSIG
and
.I arg2
is not zero or a signal number.
.SH "CONFORMING TO"
This call is Linux-specific.
IRIX has a 
.BR prctl ()
system call (also introduced in Linux 2.1.44
as irix_prctl on the MIPS architecture),
with prototype
.sp
.BI "ptrdiff_t prctl(int " option ", int " arg2 ", int " arg3 );
.sp
and options to get the maximum number of processes per user,
get the maximum number of processors the calling process can use,
find out whether a specified process is currently blocked,
get or set the maximum stack size, etc.
.SH AVAILABILITY
The 
.BR prctl () 
system call was introduced in Linux 2.1.57.
.\" The library interface was added in glibc 2.0.6
.SH "SEE ALSO"
.BR signal (2)