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Kirk McKusick c7996ddf80 Create a new GEOM utility, gunion(8). 
The gunion(8) utility is used to track changes to a read-only disk on
a writable disk. Logically, a writable disk is placed over a read-only
disk. Write requests are intercepted and stored on the writable
disk. Read requests are first checked to see if they have been
written on the top (writable disk) and if found are returned. If
they have not been written on the top disk, then they are read from
the lower disk.

The gunion(8) utility can be especially useful if you have a large
disk with a corrupted filesystem that you are unsure of how to
repair. You can use gunion(8) to place another disk over the corrupted
disk and then attempt to repair the filesystem. If the repair fails,
you can revert all the changes in the upper disk and be back to the
unchanged state of the lower disk thus allowing you to try another
approach to repairing it. If the repair is successful you can commit
all the writes recorded on the top disk to the lower disk.

Another use of the gunion(8) utility is to try out upgrades to your
system. Place the upper disk over the disk holding your filesystem
that is to be upgraded and then run the upgrade on it. If it works,
commit it; if it fails, revert the upgrade.

Further details can be found in the gunion(8) manual page.

Reviewed by: Chuck Silvers, kib (earlier version)
tested by:   Peter Holm
Differential Revision: https://reviews.freebsd.org/D32697
2022-02-28 16:36:08 -08:00
..
arpa SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
gssapi Add META_MODE support. 2015-06-13 19:20:56 +00:00
protocols Clean up global variable declarations in the dump and restore 2020-04-04 00:56:56 +00:00
rpc include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
rpcsvc Increase YPMAXRECORD to 16M to be compatible with Linux. 2019-08-12 20:27:33 +00:00
xlocale Remove 'All Rights Reserved' from xlocale FreeBSD Foundation copyrights 2021-12-16 14:29:12 -05:00
_ctype.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
a.out.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
ar.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
assert.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
bitstring.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
complex.h Implementations of cexpl() 2021-11-05 13:51:42 +02:00
cpio.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
ctype.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
db.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
dirent.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
dlfcn.h Implement RTLD_DEEPBIND. 2020-05-15 11:58:01 +00:00
elf-hints.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
elf.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
err.h Avoid implicit gcc nonnull attribute in vwarnx(). 2018-01-28 19:37:30 +00:00
fmtmsg.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
fnmatch.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
fstab.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
fts.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
ftw.h SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
getopt.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
glob.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
grp.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
gssapi.h
hesiod.h SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
iconv.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
ieeefp.h
ifaddrs.h SPDX: mostly fixes to previous changes. 2017-12-13 16:13:17 +00:00
inttypes.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
iso646.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
kenv.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
langinfo.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
libgen.h Remove basename_r(3). 2017-12-08 22:06:18 +00:00
limits.h Reduce NL_ARGMAX to 4096 to match Linux. 2018-10-04 21:55:58 +00:00
link.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
locale.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
Makefile Create a new GEOM utility, gunion(8). 2022-02-28 16:36:08 -08:00
Makefile.depend new depends 2015-06-16 23:37:19 +00:00
malloc_np.h Add memalign(3), mostly for glibc compatibility. 2020-05-14 21:12:08 +00:00
malloc.h Make include/malloc.h usable again. 2020-05-12 18:17:57 +00:00
memory.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
mk-osreldate.sh Move to using newvers -c instead of VARS_ONLY=1 2019-05-23 17:19:05 +00:00
monetary.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
mpool.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
mqueue.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
ndbm.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
netconfig.h netconfig.h: sync with upstream. 2017-11-27 17:18:31 +00:00
netdb.h Fix mismatch from r342379. 2018-12-23 20:51:13 +00:00
nl_types.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
nlist.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
nss.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
nsswitch.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
paths.h Add search of LOCALBASE/share/calendar for calendars supplied by a port. 2020-10-23 09:22:23 +00:00
printf.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
proc_service.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
pthread_np.h Revert r361770 "Add pthread_getname_np() and pthread_setname_np() aliases" for now. 2020-06-04 09:06:03 +00:00
pthread.h Reduce code duplication in machine/_types.h 2021-06-14 16:30:16 +01:00
pwd.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
ranlib.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
readpassphrase.h SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
regex.h <regex.h>: reserve a regcomp field for REG_POSIX 2020-07-31 12:40:31 +00:00
res_update.h SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
resolv.h SPDX: license IDs for some ISC-related files. 2017-12-08 15:57:29 +00:00
runetype.h Remove __NO_TLS. 2021-02-23 20:08:10 +02:00
sched.h sched.h: Use pid_t type for pid argument 2021-12-17 08:22:21 +02:00
search.h Improve typing of POSIX search tree functions. 2016-10-13 18:25:40 +00:00
semaphore.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
setjmp.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
signal.h Add sigsetop extensions commonly found in musl libc and glibc 2019-12-12 01:41:55 +00:00
spawn.h posix_spawn: add closefrom non-portable action 2021-11-30 03:43:54 +02:00
stab.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
stdalign.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
stdbool.h Remove obsolete check for GCC < 3 and support for Intel Compiler 2020-10-24 23:21:06 +00:00
stddef.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
stdio.h libc: provide fputc_unlocked 2020-02-02 19:45:12 +00:00
stdlib.h libc: add clearenv function 2021-11-07 16:20:15 +01:00
stdnoreturn.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
string.h libc: add mempcpy(3) and wmempcpy(3) 2021-07-15 19:40:28 +03:00
stringlist.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
strings.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
sysexits.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
tar.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
termios.h Add tcgetwinsize(3) and tcsetwinsize(3) to termios 2020-12-25 20:43:09 +02:00
tgmath.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
time.h time.h: reduce CLOCK_ namespace pollution, move to _clock_id.h 2021-07-30 17:20:22 -06:00
timeconv.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
timers.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
ttyent.h Improve missing tty handling in init(8). This removes a check that did 2018-02-27 10:54:15 +00:00
uchar.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
ulimit.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
unistd.h swapoff: add one more variant of the syscall 2021-12-09 02:48:46 +02:00
utime.h include: further adoption of SPDX licensing ID tags. 2017-11-20 19:45:28 +00:00
utmpx.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
uuid.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
varargs.h We don't support gcc < 4.2.1, so varargs.h now is just #error 2018-02-12 14:48:14 +00:00
wchar.h libc: add mempcpy(3) and wmempcpy(3) 2021-07-15 19:40:28 +03:00
wctype.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
wordexp.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00
xlocale.h include: General further adoption of SPDX licensing ID tags. 2017-11-25 17:09:43 +00:00