belkin@teecs.UUCP (Hershel Belkin) (06/28/90)
Forgive me if this should be obvious, but I'd like to clear up something... I have often heard/read that fsck should not be run on a mounted file system, and further, should never be run while in multi-user mode. While I understand the risks involved in attempting to use fsck to correct errors while in multi-user mode, I have a problem understanding why there should be any harm in using fsck to simply "look" at a mounted file system even while being used! I can imagine that the fsck results could be incorrect (ie. may perhaps indicate an error when in fact there is none) due to disc activity. But is there any possibility that fsck could *cause* a problem (again, assuming "-n" responses)?? I'd appreciate some insights to this question. (BTW, I have often run fsck's in this mode, only switching to single user mode if fsck shows any errors, so that I can confirm them as "real". I have never experienced any problems, but I'd like to know what others feel about this). Thanks! -- +-----------------------------------------------+-------------------------+ | Hershel Belkin hp9000/825(HP-UX)| UUCP: teecs!belkin | | Test Equipment Engineering Computing Services | Phone: 416 246-2647 | | Litton Systems Canada Limited (Toronto) | FAX: 416 246-5233 | +-----------------------------------------------+-------------------------+
cpcahil@virtech.uucp (Conor P. Cahill) (07/02/90)
In article <970007@teecs.UUCP> belkin@teecs.UUCP (Hershel Belkin) writes: >I have often heard/read that fsck should not be run on a mounted >file system, and further, should never be run while in multi-user >mode. While I understand the risks involved in attempting to >use fsck to correct errors while in multi-user mode, I have a >problem understanding why there should be any harm in using fsck >to simply "look" at a mounted file system even while being used! The only rule to remember is: FSCK should not be run on a mounted file system. This gives you problems when the root file system is involved (especially when you are on a unix system that does not provide the capability to remount root following an fsck). Single or Multi user mode has no effect on fsck. If a file system is unmounted you could fsck it until the cows come home and have no problems with your system (the execption being, of course, disk i/o performance). >I can imagine that the fsck results could be incorrect (ie. may >perhaps indicate an error when in fact there is none) due to >disc activity. But is there any possibility that fsck could >*cause* a problem (again, assuming "-n" responses)?? If you run fsck in a "read only" mode, it will not cause any problems. Like you said, it will (almost positively) report false errors on your file system. >I'd appreciate some insights to this question. (BTW, I have often >run fsck's in this mode, only switching to single user mode if >fsck shows any errors, so that I can confirm them as "real". I have >never experienced any problems, but I'd like to know what others >feel about this). Thanks! I would recommend against running fsck on a mounted file system even if you are now carefull to answer n to all the update questions. Some time in the future you will forget the n and cause file system damage that you will regret. If you want to check a file system, umount the file system and fsck it. -- Conor P. Cahill (703)430-9247 Virtual Technologies, Inc., uunet!virtech!cpcahil 46030 Manekin Plaza, Suite 160 Sterling, VA 22170
donlash@uncle.uucp (Donald Lashomb) (07/03/90)
In article <970007@teecs.UUCP> belkin@teecs.UUCP (Hershel Belkin) writes: > >I have often heard/read that fsck should not be run on a mounted >file system, and further, should never be run while in multi-user [...] >disc activity. But is there any possibility that fsck could >*cause* a problem (again, assuming "-n" responses)?? [...] I see no problem as long as you use "fsck -n". Make sure you use the "-n" option on the command line, don't depend on manually answering "No" to fsck's questions to protect your filesystem from changes. On my system, if fsck is run without the "-n" option, it makes some changes to the filesystem even if you answer "No" to all its questions ( clears empty files, If memory serves ). Using the "-n" command line option, fsck announces "Read-only mode" upon startup. I assume, it therefore will not make any changes to the filesystem, no matter what. BTW- I also run fsck on my root (mounted of course) filesystem regularly. I do this this in single-user mode, however. I do an immediate reboot after running fsck. In fact, fsck forces an immediate reboot under some conditions (eg using "fsck -S" to cleanup the freelist). -Don donlash@uncle.UUCP
peter@ficc.ferranti.com (Peter da Silva) (07/06/90)
In article <1990Jul02.124310.7848@virtech.uucp> cpcahil@virtech.UUCP (Conor P. Cahill) writes: > FSCK should not be run on a mounted file system. Always proscribed, occasionally mandatory. Once or twice in my life I've had to run fsck on a mounted non-root file system. A quiescent one, to be sure. Sometimes you just can't unmount a file system, and you can't risk a reboot just then... Scarey, and you should reboot and re-fsck to rebuild the free list before doing any real work on it... but it's possible. If I never have to do it again, though, that'll still be too soon. -- Peter da Silva. `-_-' +1 713 274 5180. <peter@ficc.ferranti.com>