libc/sys/procctl.2

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.Dd August 21, 2015
.Dt PROCCTL 2
.Os
.Sh NAME
.Nm procctl
.Nd control processes
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/procctl.h
.Ft int
.Fn procctl "idtype_t idtype" "id_t id" "int cmd" "void *arg"
.Sh DESCRIPTION
The
.Fn procctl
system call provides for control over processes.
The
.Fa idtype
and
.Fa id
arguments specify the set of processes to control.
If multiple processes match the identifier,
.Nm
will make a
.Dq best effort
to control as many of the selected processes as possible.
An error is only returned if no selected processes successfully complete
the request.
The following identifier types are supported:
.Bl -tag -width "Dv P_PGID"
.It Dv P_PID
Control the process with the process ID
.Fa id .
.It Dv P_PGID
Control processes belonging to the process group with the ID
.Fa id .
.El
.Pp
The control request to perform is specified by the
.Fa cmd
argument.
The following commands are supported:
.Bl -tag -width "PROC_REAP_GETPIDS"
.It Dv PROC_SPROTECT
Set process protection state.
This is used to mark a process as protected from being killed if the system
exhausts the available memory and swap.
The
.Fa arg
parameter must point to an integer containing an operation and zero or more
optional flags.
The following operations are supported:
.Bl -tag -width "Dv PPROT_CLEAR"
.It Dv PPROT_SET
Mark the selected processes as protected.
.It Dv PPROT_CLEAR
Clear the protected state of selected processes.
.El
.Pp
The following optional flags are supported:
.Bl -tag -width "Dv PPROT_DESCEND"
.It Dv PPROT_DESCEND
Apply the requested operation to all child processes of each selected process
in addition to each selected process.
.It Dv PPROT_INHERIT
When used with
.Dv PPROT_SET ,
mark all future child processes of each selected process as protected.
Future child processes will also mark all of their future child processes.
.El
.It Dv PROC_REAP_ACQUIRE
Acquires the reaper status for the current process.
Reaper status means that children orphaned by the reaper's descendants
that were forked after the acquisition of reaper status are reparented to the
reaper process.
After system initialization,
.Xr init 8
is the default reaper.
.It Dv PROC_REAP_RELEASE
Release the reaper state for the current process.
The reaper of the current process becomes the new reaper of the
current process's descendants.
.It Dv PROC_REAP_STATUS
Provides information about the reaper of the specified process,
or the process itself when it is a reaper.
The
.Fa data
argument must point to a
.Vt procctl_reaper_status
structure which is filled in by the syscall on successful return.
.Bd -literal
struct procctl_reaper_status {
	u_int	rs_flags;
	u_int	rs_children;
	u_int	rs_descendants;
	pid_t	rs_reaper;
	pid_t	rs_pid;
};
.Ed
The
.Fa rs_flags
may have the following flags returned:
.Bl -tag -width "Dv REAPER_STATUS_REALINIT"
.It Dv REAPER_STATUS_OWNED
The specified process has acquired reaper status and has not
released it.
When the flag is returned, the specified process
.Fa id ,
pid, identifies the reaper, otherwise the
.Fa rs_reaper
field of the structure is set to the pid of the reaper
for the specified process id.
.It Dv REAPER_STATUS_REALINIT
The specified process is the root of the reaper tree, i.e.,
.Xr init 8 .
.El
.Pp
The
.Fa rs_children
field returns the number of children of the reaper among the descendants.
It is possible to have a child whose reaper is not the specified process,
since the reaper for any existing children is not reset on the
.Dv PROC_REAP_ACQUIRE
operation.
The
.Fa rs_descendants
field returns the total number of descendants of the reaper(s),
not counting descendants of the reaper in the subtree.
The
.Fa rs_reaper
field returns the reaper pid.
The
.Fa rs_pid
returns the pid of one reaper child if there are any descendants.
.It Dv PROC_REAP_GETPIDS
Queries the list of descendants of the reaper of the specified process.
The request takes a pointer to a
.Vt procctl_reaper_pids
structure in the
.Fa data
parameter.
.Bd -literal
struct procctl_reaper_pids {
	u_int	rp_count;
	struct procctl_reaper_pidinfo *rp_pids;
};
.Ed
When called, the
.Fa rp_pids
field must point to an array of
.Vt procctl_reaper_pidinfo
structures, to be filled in on return,
and the
.Fa rp_count
field must specify the size of the array,
into which no more than
.Fa rp_count
elements will be filled in by the kernel.
.Pp
The
.Vt "struct procctl_reaper_pidinfo"
structure provides some information about one of the reaper's descendants.
Note that for a descendant that is not a child, it may be incorrectly
identified because of a race in which the original child process exited
and the exited process's pid was reused for an unrelated process.
.Bd -literal
struct procctl_reaper_pidinfo {
	pid_t	pi_pid;
	pid_t	pi_subtree;
	u_int	pi_flags;
};
.Ed
The
.Fa pi_pid
field is the process id of the descendant.
The
.Fa pi_subtree
field provides the pid of the child of the reaper, which is the (grand-)parent
of the process.
The
.Fa pi_flags
field returns the following flags, further describing the descendant:
.Bl -tag -width "Dv REAPER_PIDINFO_VALID"
.It Dv REAPER_PIDINFO_VALID
Set to indicate that the
.Vt procctl_reaper_pidinfo
structure was filled in by the kernel.
Zero-filling the
.Fa rp_pids
array and testing the
.Dv REAPER_PIDINFO_VALID
flag allows the caller to detect the end
of the returned array.
.It Dv REAPER_PIDINFO_CHILD
The
.Fa pi_pid
field identifies the direct child of the reaper.
.El
.It Dv PROC_REAP_KILL
Request to deliver a signal to some subset of the descendants of the reaper.
The
.Fa data
parameter must point to a
.Vt procctl_reaper_kill
structure, which is used both for parameters and status return.
.Bd -literal
struct procctl_reaper_kill {
	int	rk_sig;
	u_int	rk_flags;
	pid_t	rk_subtree;
	u_int	rk_killed;
	pid_t	rk_fpid;
};
.Ed
The
.Fa rk_sig
field specifies the signal to be delivered.
Zero is not a valid signal number, unlike for
.Xr kill 2 .
The
.Fa rk_flags
field further directs the operation.
It is or-ed from the following flags:
.Bl -tag -width "Dv REAPER_KILL_CHILDREN"
.It Dv REAPER_KILL_CHILDREN
Deliver the specified signal only to direct children of the reaper.
.It Dv REAPER_KILL_SUBTREE
Deliver the specified signal only to descendants that were forked by
the direct child with pid specified in the
.Fa rk_subtree
field.
.El
If neither the
.Dv REAPER_KILL_CHILDREN
nor the
.Dv REAPER_KILL_SUBTREE
flags are specified, all current descendants of the reaper are signalled.
.Pp
If a signal was delivered to any process, the return value from the request
is zero.
In this case, the
.Fa rk_killed
field identifies the number of processes signalled.
The
.Fa rk_fpid
field is set to the pid of the first process for which signal
delivery failed, e.g., due to permission problems.
If no such process exists, the
.Fa rk_fpid
field is set to -1.
.It Dv PROC_TRACE_CTL
Enable or disable tracing of the specified process(es), according to the
value of the integer argument.
Tracing includes attachment to the process using the
.Xr ptrace 2
and
.Xr ktrace 2 ,
debugging sysctls,
.Xr hwpmc 4 ,
.Xr dtrace 1 ,
and core dumping.
Possible values for the
.Fa data
argument are:
.Bl -tag -width "Dv PROC_TRACE_CTL_DISABLE_EXEC"
.It Dv PROC_TRACE_CTL_ENABLE
Enable tracing, after it was disabled by
.Dv PROC_TRACE_CTL_DISABLE .
Only allowed for self.
.It Dv PROC_TRACE_CTL_DISABLE
Disable tracing for the specified process.
Tracing is re-enabled when the process changes the executing
program with the
.Xr execve 2
syscall.
A child inherits the trace settings from the parent on
.Xr fork 2 .
.It Dv PROC_TRACE_CTL_DISABLE_EXEC
Same as
.Dv PROC_TRACE_CTL_DISABLE ,
but the setting persists for the process even after
.Xr execve 2 .
.El
.It Dv PROC_TRACE_STATUS
Returns the current tracing status for the specified process in
the integer variable pointed to by
.Fa data .
If tracing is disabled,
.Fa data
is set to -1.
If tracing is enabled, but no debugger is attached by the
.Xr ptrace 2
syscall,
.Fa data
is set to 0.
If a debugger is attached,
.Fa data
is set to the pid of the debugger process.
.El
.Sh NOTES
Disabling tracing on a process should not be considered a security
feature, as it is bypassable both by the kernel and privileged processes,
and via other system mechanisms.
As such, it should not be utilized to reliably protect cryptographic
keying material or other confidential data.
.Sh RETURN VALUES
If an error occurs, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn procctl
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa arg
parameter points outside the process's allocated address space.
.It Bq Er EINVAL
The
.Fa cmd
argument specifies an unsupported command.
.Pp
The
.Fa idtype
argument specifies an unsupported identifier type.
.It Bq Er EPERM
The calling process does not have permission to perform the requested
operation on any of the selected processes.
.It Bq Er ESRCH
No processes matched the requested
.Fa idtype
and
.Fa id .
.It Bq Er EINVAL
An invalid operation or flag was passed in
.Fa arg
for a
.Dv PROC_SPROTECT
command.
.It Bq Er EPERM
The
.Fa idtype
argument is not equal to
.Dv P_PID ,
or
.Fa id
is not equal to the pid of the calling process, for
.Dv PROC_REAP_ACQUIRE
or
.Dv PROC_REAP_RELEASE
requests.
.It Bq Er EINVAL
Invalid or undefined flags were passed to a
.Dv PROC_REAP_KILL
request.
.It Bq Er EINVAL
An invalid or zero signal number was requested for a
.Dv PROC_REAP_KILL
request.
.It Bq Er EINVAL
The
.Dv PROC_REAP_RELEASE
request was issued by the
.Xr init 8
process.
.It Bq Er EBUSY
The
.Dv PROC_REAP_ACQUIRE
request was issued by a process that had already acquired reaper status
and has not yet released it.
.It Bq Er EBUSY
The
.Dv PROC_TRACE_CTL
request was issued for a process already being traced.
.It Bq Er EPERM
The
.Dv PROC_TRACE_CTL
request to re-enable tracing of the process
.Po Dv PROC_TRACE_CTL_ENABLE Pc ,
or to disable persistence of
.Dv PROC_TRACE_CTL_DISABLE
on
.Xr execve 2
was issued for a non-current process.
.It Bq Er EINVAL
The value of the integer
.Fa data
parameter for the
.Dv PROC_TRACE_CTL
request is invalid.
.El
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr kill 2 ,
.Xr ktrace 2 ,
.Xr ptrace 2 ,
.Xr wait 2 ,
.Xr hwpmc 4 ,
.Xr init 8
.Sh HISTORY
The
.Fn procctl
function appeared in
.Fx 10.0 .
The reaper facility is based on a similar feature of Linux and
DragonflyBSD, and first appeared in
.Fx 10.2 .