send a message to syslogd
char *msg, size_t
function is used to transmit a
formatted message direct to
syslogd(8) without requiring the allocation of a socket. The
msg is not NUL terminated and its
len is limited to 8192 bytes. If
LOG_CONS is specified in the
flags argument, and
syslogd(8) is not accepting messages, the message will be sent to the
console. This is used internally by
syslog_r(3), so that messages can be sent during difficult
situations. If sending to
syslogd(8) fails, up to 100 messages are stashed in the kernel. After
that, dropped messages are counted. When
syslogd(8) works again, before the next message, stashed messages and
possibly a warning with the drop counter, error number, and pid is
To receive messages from the kernel,
syslogd(8) has to create a datagram socket pair and register one end.
This registration is done by opening the /dev/klog
device and passing one file descriptor of the socket pair as argument to
LIOCSFD invoked on the klog file descriptor. After
that the messages can be read from the other end of the socket pair. By
utilizing /dev/klog the access to log messages is
limited to processes that may open this device.
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
sendsyslog() can fail if:
- An invalid user space address was specified for a parameter.
- The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.
- The system was unable to allocate an internal buffer. The operation may succeed when buffers become available.
- The message cannot be sent, likely because syslogd(8) is not running.
sendsyslog() function call appeared in
OpenBSD 5.6. The flags
argument was added in OpenBSD 6.0.