.\"	$OpenBSD: sendsyslog.2,v 1.13 2021/03/09 15:08:23 bluhm Exp $
.\"
.\" Copyright (c) 2017 Alexander Bluhm <bluhm@openbsd.org>
.\" Copyright (c) 2014 Theo de Raadt
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\"
.Dd $Mdocdate: March 9 2021 $
.Dt SENDSYSLOG 2
.Os
.Sh NAME
.Nm sendsyslog
.Nd send a message to syslogd
.Sh SYNOPSIS
.In sys/syslog.h
.In sys/types.h
.Ft int
.Fn sendsyslog "const char *msg" "size_t len" "int flags"
.Sh DESCRIPTION
The
.Fn sendsyslog
function is used to transmit a
.Xr syslog 3
formatted message direct to
.Xr syslogd 8
without requiring the allocation of a socket.
The
.Fa msg
is not NUL terminated and its
.Fa len
is limited to 8192 bytes.
If
.Dv LOG_CONS
is specified in the
.Fa flags
argument, and
.Xr syslogd 8
is not accepting messages, the message will be sent to the console.
This is used internally by
.Xr syslog_r 3 ,
so that messages can be sent during difficult situations.
If sending to
.Xr syslogd 8
fails, up to 100 messages are stashed in the kernel.
After that, dropped messages are counted.
When
.Xr syslogd 8
works again, before the next message, stashed messages and possibly
a warning with the drop counter, error number, and pid is logged.
.Pp
To receive messages from the kernel,
.Xr syslogd 8
has to create a datagram socket pair and register one end.
This registration is done by opening the
.Pa /dev/klog
device and passing one file descriptor of the socket pair as argument
to
.Xr ioctl 2 Dv LIOCSFD
invoked on the klog file descriptor.
After that the messages can be read from the other end of the
socket pair.
By utilizing
.Pa /dev/klog
the access to log messages is limited to processes that may open
this device.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn sendsyslog
can fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
An invalid user space address was specified for a parameter.
.It Bq Er EMSGSIZE
The socket requires that message be sent atomically,
and the size of the message to be sent made this impossible.
.It Bq Er ENOBUFS
The system was unable to allocate an internal buffer.
The operation may succeed when buffers become available.
.It Bq Er ENOTCONN
The message cannot be sent, likely because
.Xr syslogd 8
is not running.
.El
.Sh SEE ALSO
.Xr syslog_r 3 ,
.Xr syslogd 8
.Sh HISTORY
The
.Fn sendsyslog
function call appeared in
.Ox 5.6 .
The
.Fa flags
argument was added in
.Ox 6.0 .