4 files changed, 156 insertions, 0 deletions
diff --git a/bin/sync/Makefile b/bin/sync/Makefile
new file mode 100644
index 000000000000..dd3460afcbe8
--- /dev/null
+++ b/bin/sync/Makefile
@@ -0,0 +1,5 @@
+PACKAGE=runtime
+PROG=	sync
+MAN=	sync.8
+
+.include <bsd.prog.mk>
diff --git a/bin/sync/Makefile.depend b/bin/sync/Makefile.depend
new file mode 100644
index 000000000000..93249906da4f
--- /dev/null
+++ b/bin/sync/Makefile.depend
@@ -0,0 +1,14 @@
+# Autogenerated - do NOT edit!
+
+DIRDEPS = \
+	include \
+	lib/${CSU_DIR} \
+	lib/libc \
+	lib/libcompiler_rt \
+
+
+.include <dirdeps.mk>
+
+.if ${DEP_RELDIR} == ${_DEP_RELDIR}
+# local dependencies - needed for -jN in clean tree
+.endif
diff --git a/bin/sync/sync.8 b/bin/sync/sync.8
new file mode 100644
index 000000000000..fcd07ca72240
--- /dev/null
+++ b/bin/sync/sync.8
@@ -0,0 +1,99 @@
+.\"-
+.\" Copyright (c) 1980, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd April 25, 2024
+.Dt SYNC 8
+.Os
+.Sh NAME
+.Nm sync
+.Nd force completion of pending disk writes (flush cache)
+.Sh SYNOPSIS
+.Nm
+.Sh DESCRIPTION
+The
+.Nm
+utility
+can be called to ensure that all disk writes have been completed before the
+processor is halted in a way not suitably done by
+.Xr reboot 8
+or
+.Xr halt 8 .
+Generally, it is preferable to use
+.Xr reboot 8
+or
+.Xr halt 8
+to shut down the system,
+as they may perform additional actions
+such as resynchronizing the hardware clock
+and flushing internal caches before performing a final
+.Nm .
+.Pp
+The
+.Nm
+utility utilizes the
+.Xr sync 2
+function call.
+.Sh SEE ALSO
+.Xr fsync 2 ,
+.Xr sync 2 ,
+.Xr syncer 4 ,
+.Xr halt 8 ,
+.Xr reboot 8
+.Sh HISTORY
+A
+.Nm
+utility appeared in
+.At v4 .
+.Pp
+On systems older than
+.Bx 4.0 ,
+commands like
+.Xr reboot 8
+and
+.Xr halt 8
+were unavailable.
+The shutdown procedure involved running
+.Nm ,
+waiting for the lights to stop,
+and turning off the machine.
+.Pp
+Issuing three separate
+.Nm
+commands (one line each) was a placebo that would generally suffice in
+.At v7
+machines that were otherwise quiesced systems.
+It replaced the one-per-line
+.Nm
+as a substitute for waiting.
+.Pp
+.Bx 4.0
+introduced
+.Xr reboot 2
+and
+.Xr sync 2
+which rendered this trick obsolete.
diff --git a/bin/sync/sync.c b/bin/sync/sync.c
new file mode 100644
index 000000000000..7560e794d35f
--- /dev/null
+++ b/bin/sync/sync.c
@@ -0,0 +1,38 @@
+/*-
+ * Copyright (c) 1987, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+
+int
+main(int argc __unused, char *argv[] __unused)
+{
+	sync();
+	exit(0);
+}