confusing /etc/fstab

[Robert Storey]

I'm very curious (and not entirely pleased) by how different /etc/fstab
is in Fedora when compared to almost any other Linux distro I've used.
For example, the following is a fairly complex /etc/fstab from an old
version of SuSE:

# Device	Mountpoint	FStype	Options		Dump	fsckorder#
/dev/hda1	none		swap	defaults	0	0
/dev/hda2	/		ext2	defaults	1	1
/dev/hda3	/boot		ext2	defaults	2	2
/dev/hda5	/home		ext2	defaults	2	2
/dev/hda6	/tmp		ext2	defaults	2	2
/dev/hda7	/usr		ext2	defaults	2	2
/dev/hda8	/var		ext2	defaults	2	2
/dev/hdc	/cdrom		cd9660	ro,noauto	0	0
/dev/hdd	/cdrom1		cd9660	ro,noauto	0	0


Now compare that to my current FC3 installation:

# This file is edited by fstab-sync - see 'man fstab-sync' for details
LABEL=/1                /                       ext3    defaults       
1 1
none                    /dev/pts                devpts  gid=5,mode=620 
0 0
none                    /dev/shm                tmpfs   defaults       
0 0
none                    /proc                   proc    defaults       
0 0
none                    /sys                    sysfs   defaults       
0 0
LABEL=SWAP-hda2         swap                    swap    defaults       
0 0
/dev/hdd                /media/cdrecorder       auto   
pamconsole,ro,exec,noauto,managed 0 0
/dev/hdc                /media/cdrecorder2      auto   
pamconsole,ro,exec,noauto,managed 0 0


What's confusing to me here is that, in Fedora, I can't figure out which
partition is mounted where. Is my / partition /dev/hda3, or /dev/hda5,
or ???   Ditto for swap, or any other partition. If I wanted to make
some change in the partition table (for example, adding a /home
partition) I have no idea how I could get /etc/fstab to recognize it.

I've tried making some sense out of fstab-sync, but so far it's pretty
opague. Where does Fedora store the partition information? Anybody know
some links that can explain this messy filesystem table?

Thanks in advance,
Robert

[Paul Howarth]

Robert Storey wrote:
>  What's confusing to me here is that, in Fedora, I can't
> figure out which
>  partition is mounted where. Is my / partition /dev/hda3, or /dev/hda5,
>  or ???   Ditto for swap, or any other partition. If I wanted to make
>  some change in the partition table (for example, adding a /home
>  partition) I have no idea how I could get /etc/fstab to recognize it.
>  
>  I've tried making some sense out of fstab-sync, but so far it's pretty
>  opague. Where does Fedora store the partition information? Anybody know
>  some links that can explain this messy filesystem table? 
If you just run the command "mount" (you don't have to be root), you'll

see which partitions are mounted where. You can use either hardcoded 
partition names such as "/dev/hda7" or filesystem label references such 
as "LABEL=/home" in /etc/fstab; either will work OK. You can assign a 
label to a partition when you create the filesystem on it by using the 
-L option in mke2fs, and you can set or change the label of an existing 
partition using the -L option in tune2fs.

Paul.

[Paul Almquist]

On Monday 31 January 2005 07:35, Paul Howarth wrote:
>  Robert Storey wrote:
>  > What's confusing to me here is that, in Fedora, I can't figure out which
>  > partition is mounted where. Is my / partition /dev/hda3, or /dev/hda5,
>  > or ???   Ditto for swap, or any other partition. If I wanted to make
>  > some change in the partition table (for example, adding a /home
>  > partition) I have no idea how I could get /etc/fstab to recognize it.
>  >
>  > I've tried making some sense out of fstab-sync, but so far it's pretty
>  > opague. Where does Fedora store the partition information? Anybody know
>  > some links that can explain this messy filesystem table?
>
>  If you just run the command "mount" (you don't have to be root),
> you'll
>  see which partitions are mounted where. You can use either hardcoded
>  partition names such as "/dev/hda7" or filesystem label references such
>  as "LABEL=/home" in /etc/fstab; either will work OK. You can assign a
>  label to a partition when you create the filesystem on it by using the
>  -L option in mke2fs, and you can set or change the label of an existing
>  partition using the -L option in tune2fs.
>  
or display and change labels with e2label

But why label in the first place?  I wondered about that for a while and came 
to this conclusion:  If a drive in an Intel-like box is changed from master 
to slave or primary IDE channel to secondary or some other combination then 
the device name changes, e.g., /dev/hda1 to /dev/hdb1.  When booting after 
this change without fixing /etc/fstab, mount cannot find /dev/hda1 because of 
its new location at /dev/hdb1.  By labeling partitions and using the labels 
in /etc/fstab, mount will search all available partitions for the one with 
the name specified in /etc/fstab (or mount command).  This eliminates the 
problem of device names changing  when modifying the drive configuration.

Labeling does introduce a problem:  What happens if 2 partitions have the same 
label?  Which one does mount choose?  I do not know the algorithm but I do 
know that mount does not know which one you want to use.  In the technical 
college where I taught Unix/Linux system administration we had removable IDE 
drives in our lab machines. (standard IDE drives in a tray that slides into a 
bay the in cabinet.  works good.  I use them at home too)  I had a removable 
drive bay on my office machine. A couple of times I had to make some repairs 
to corrupted student drives.  Since the drives are not hot-swappable   I 
would power down my machine, insert the student's drive, power up and boot.  
Their partition labels were the same as on my internal IDE drive and as a 
result would bet mounted instead of my partitions.  After a couple time of 
messing with that I changed the /etc/fstab file on my system to use device 
names instead of labels.

fsck also recognizes the labels, probably other disk related commands  too.

paul
-- 
Paul F. Almquist
paul(a)almquist.name
Eau Claire, WI  USA

[Pedro Fernandes Macedo]

Paul F. Almquist wrote:

> Labeling does introduce a problem:  What happens if 2 partitions have
> the same 
> label?  Which one does mount choose?  I do not know the algorithm but I do 
> know that mount does not know which one you want to use.  In the technical 
> college where I taught Unix/Linux system administration we had removable IDE 
> drives in our lab machines. (standard IDE drives in a tray that slides into a 
> bay the in cabinet.  works good.  I use them at home too)  I had a removable 
> drive bay on my office machine. A couple of times I had to make some repairs 
> to corrupted student drives.  Since the drives are not hot-swappable   I 
> would power down my machine, insert the student's drive, power up and boot.  
> Their partition labels were the same as on my internal IDE drive and as a 
> result would bet mounted instead of my partitions.  After a couple time of 
> messing with that I changed the /etc/fstab file on my system to use device 
> names instead of labels.
>
> fsck also recognizes the labels, probably other disk related commands  too.
>
> paul
>   
>  
In such cases , I strongly suggest changing the labels. Here I used to 
have FC2 and FC3 test releases (during FC3 test) installed.
The root for FC2 was labeled / , the one for FC3 was labeled fc3/ . And 
the same way for other partitions.
Now , if you need to insert another disk with the same labels , you can 
always change the root=LABEL=/ part on grub to point to the right device.
This change can be done at boot time (just press "a" on grub screen) and 
it probably will fix the issue, since the kernel will know exactly which 
partition to use on boot time.

--
Pedro Macedo

[Paul Almquist]

On Monday 31 January 2005 13:33, Pedro Fernandes Macedo wrote:
>  Paul F. Almquist wrote:
>  >Labeling does introduce a problem:  What happens if 2 partitions have the
>  > same label?  Which one does mount choose?  I do not know the algorithm
>  > but I do know that mount does not know which one you want to use.  In the
>  > technical college where I taught Unix/Linux system administration we had
>  > removable IDE drives in our lab machines. (standard IDE drives in a tray
>  > that slides into a bay the in cabinet.  works good.  I use them at home
>  > too)  I had a removable drive bay on my office machine. A couple of times
>  > I had to make some repairs to corrupted student drives.  Since the drives
>  > are not hot-swappable   I would power down my machine, insert the
>  > student's drive, power up and boot. Their partition labels were the same
>  > as on my internal IDE drive and as a result would bet mounted instead of
>  > my partitions.  After a couple time of messing with that I changed the
>  > /etc/fstab file on my system to use device names instead of labels.
>  >
>  >fsck also recognizes the labels, probably other disk related commands 
>  > too.
>  >
>  >paul
>
>  In such cases , I strongly suggest changing the labels. Here I used to
>  have FC2 and FC3 test releases (during FC3 test) installed.
>  The root for FC2 was labeled / , the one for FC3 was labeled fc3/ . And
>  the same way for other partitions.
>  Now , if you need to insert another disk with the same labels , you can
>  always change the root=LABEL=/ part on grub to point to the right device.
>  This change can be done at boot time (just press "a" on grub screen) and
>  it probably will fix the issue, since the kernel will know exactly which
>  partition to use on boot time. 
That would take care of getting the right root
partition but what about the 
case where, for example, /usr was in a separate partition on each disk with 
the same labels?

Fortunately I rarely had to deal with the problem and since I retired last May 
I won't likely run into to it again.

paul
-- 
Paul F. Almquist
paul(a)almquist.name
Eau Claire, WI  USA

[Jeff Vian]

On Mon, 2005-01-31 at 15:32 -0600, Paul F. Almquist wrote:
>  On Monday 31 January 2005 13:33, Pedro Fernandes Macedo wrote:
>  > Paul F. Almquist wrote:
>  > >Labeling does introduce a problem:  What happens if 2 partitions have the
>  > > same label?  Which one does mount choose?  I do not know the algorithm 
It
doesn't.  The conflict cannot be resolved, and it will hang

>  > > but I do know that mount does not know which one you want
> to use.  In the
>  > > technical college where I taught Unix/Linux system administration we had
>  > > removable IDE drives in our lab machines. (standard IDE drives in a tray
>  > > that slides into a bay the in cabinet.  works good.  I use them at home
>  > > too)  I had a removable drive bay on my office machine. A couple of times
>  > > I had to make some repairs to corrupted student drives.  Since the drives
>  > > are not hot-swappable   I would power down my machine, insert the
>  > > student's drive, power up and boot. Their partition labels were the same
>  > > as on my internal IDE drive and as a result would bet mounted instead of
>  > > my partitions.  After a couple time of messing with that I changed the
>  > > /etc/fstab file on my system to use device names instead of labels.
>  > >
>  > >fsck also recognizes the labels, probably other disk related commands 
>  > > too.
>  > >
>  > >paul
>  >
>  > In such cases , I strongly suggest changing the labels. Here I used to
>  > have FC2 and FC3 test releases (during FC3 test) installed.
>  > The root for FC2 was labeled / , the one for FC3 was labeled fc3/ . And
>  > the same way for other partitions.
>  > Now , if you need to insert another disk with the same labels , you can
>  > always change the root=LABEL=/ part on grub to point to the right device.
>  > This change can be done at boot time (just press "a" on grub screen) and
>  > it probably will fix the issue, since the kernel will know exactly which
>  > partition to use on boot time.
>  That would take care of getting the right root partition but what about the 
>  case where, for example, /usr was in a separate partition on each disk with 
>  the same labels?
>   
It is for that reason, that I seldom use labels.
A machine that has drives already labeled at boot time will give new
partitions created new labels. Swapping different drives in with
conflicting labels will always cause a problem when labels are used in
fstab for mounting.

I always put the partition name in fstab instead of using labels and
thus do not have the conflict.

In general, different partitions with the same label will always
conflict when labels are used.

>  Fortunately I rarely had to deal with the problem and since I retired
> last May 
>  I won't likely run into to it again.
>  
>  paul
>  -- 
>  Paul F. Almquist
>  paul(a)almquist.name
>  Eau Claire, WI  USA
>

[Paul Howarth]

On Mon, 2005-01-31 at 19:20 -0600, Jeff Vian wrote:
>  On Mon, 2005-01-31 at 15:32 -0600, Paul F. Almquist wrote:
>  > On Monday 31 January 2005 13:33, Pedro Fernandes Macedo wrote:
>  > > Paul F. Almquist wrote:
>  > > >Labeling does introduce a problem:  What happens if 2 partitions have the
>  > > > same label?  Which one does mount choose?  I do not know the algorithm
>  It doesn't.  The conflict cannot be resolved, and it will hang
>  
>  > > > but I do know that mount does not know which one you want to use.  In the
>  > > > technical college where I taught Unix/Linux system administration we had
>  > > > removable IDE drives in our lab machines. (standard IDE drives in a tray
>  > > > that slides into a bay the in cabinet.  works good.  I use them at home
>  > > > too)  I had a removable drive bay on my office machine. A couple of times
>  > > > I had to make some repairs to corrupted student drives.  Since the drives
>  > > > are not hot-swappable   I would power down my machine, insert the
>  > > > student's drive, power up and boot. Their partition labels were the
> same
>  > > > as on my internal IDE drive and as a result would bet mounted instead of
>  > > > my partitions.  After a couple time of messing with that I changed the
>  > > > /etc/fstab file on my system to use device names instead of labels.
>  > > >
>  > > >fsck also recognizes the labels, probably other disk related commands 
>  > > > too.
>  > > >
>  > > >paul
>  > >
>  > > In such cases , I strongly suggest changing the labels. Here I used to
>  > > have FC2 and FC3 test releases (during FC3 test) installed.
>  > > The root for FC2 was labeled / , the one for FC3 was labeled fc3/ . And
>  > > the same way for other partitions.
>  > > Now , if you need to insert another disk with the same labels , you can
>  > > always change the root=LABEL=/ part on grub to point to the right device.
>  > > This change can be done at boot time (just press "a" on grub screen)
> and
>  > > it probably will fix the issue, since the kernel will know exactly which
>  > > partition to use on boot time.
>  > That would take care of getting the right root partition but what about the 
>  > case where, for example, /usr was in a separate partition on each disk with 
>  > the same labels?
>  > 
>  
>  It is for that reason, that I seldom use labels.
>  A machine that has drives already labeled at boot time will give new
>  partitions created new labels. Swapping different drives in with
>  conflicting labels will always cause a problem when labels are used in
>  fstab for mounting.
>  
>  I always put the partition name in fstab instead of using labels and
>  thus do not have the conflict. 
Swapping drives around when you have hard-coded partition names in fstab
will also cause problems; drives can change device names and then not be
mountable. The gist of it is that if you're adding in extra drives (and
particularly if you're removing drives), you'd better know what you're
doing or you could have problems. The same goes for adding and removing
partitions, though filesystem labels are a bit more robust than
partition names in that case.

Paul.
-- 
Paul Howarth <paul(a)city-fan.org&gt;

[Jeff Vian]

On Wed, 2005-02-02 at 21:30 -0600, jim branagan wrote:
>  > > Labeling does introduce a problem:  What happens if 2
> partitions have the same label?  Which one does mount choose?  I do not know the
> algorithm
>  > >     
>  > > It doesn't.  The conflict cannot be resolved, and it will hang
>  Actually it says 'press any key to continue' but that just reboots
>  with the same problem.
>  > > > > In such cases , I strongly suggest changing the labels. Here I used
> to
>  > > > > have FC2 and FC3 test releases (during FC3 test) installed.
>  > > > > The root for FC2 was labeled / , the one for FC3 was labeled fc3/ .
> And
>  > > > > the same way for other partitions.
>  > > > > Now , if you need to insert another disk with the same labels , you
> can
>  > > > > always change the root=LABEL=/ part on grub to point to the right
> device.
>  > > > > This change can be done at boot time (just press "a" on
> grub screen) and
>  > > > > it probably will fix the issue, since the kernel will know exactly
> which
>  > > > > partition to use on boot time.
>  > > > >         
>  > > > That would take care of getting the right root partition but what about
> the 
>  > > > case where, for example, /usr was in a separate partition on each disk
> with 
>  > > > the same labels?
>  Even if you use only hard-coded device names in /etc/fstab
>  and /boot/grub/grub.conf, linux will crap out and dump you into run
>  level 3 if there are any duplicate labels  
This is bull!
I have often had multiple disks that are labeled the same
(especially /boot and /) and as long as I have the device names in fstab
and grub.conf I have never had a problem.

>  > > It is for that reason, that I seldom use labels.
>  > > A machine that has drives already labeled at boot time will give new
>  > > partitions created new labels. Swapping different drives in with
>  > > conflicting labels will always cause a problem when labels are used in
>  > > fstab for mounting.
>  > > 
>  > > I always put the partition name in fstab instead of using labels and
>  > > thus do not have the conflict.
>  > >     
>  > 
>  > Swapping drives around when you have hard-coded partition names in fstab
>  > will also cause problems; drives can change device names and then not be
>  > mountable. The gist of it is that if you're adding in extra drives (and
>  > particularly if you're removing drives), you'd better know what you're
>  > doing or you could have problems. The same goes for adding and removing
>  > partitions, though filesystem labels are a bit more robust than
>  > partition names in that case.
>  > 
>  > Paul.
>  >   
>  Swapping drives around between PC's always requires fstab changes with
>  or without labels; otherwise EIDE devices never change names unless
>  they are physically moved to a different IDE bus or switched between
>  master and slave.   
Often, but not always.  If the drive is moved from primary
master in one
machine to the same location in the other, no changes are required.  the
same applies to any ide bus location as long as it is moved to the
identical location on the second machine.

>  I agree labels are useful for USB and Firewire drives, but they
> should
>  probably never be labeled with names like '/' and '/tmp' that are
>  likely to be reused on many different drives.  Unfortunately the
>  Fedora installers (FC1, FC2 and FC3) like to create multiple
>  partitions with just these sorts of labels - ONCE it created a partion
>  labeled '/1', but most times I've ended up with a difficult to boot
>  machine with multiple 'LABEL=/' partitions.
>   
In my experience, IF the previously labeled drive is in the system and
you do another install it will ALWAYS label the new / as /1 ( or
rather /n where n is the next unused number).  The new labels are also
used in fstab and grub.conf so there is no problem.

If the labeled drive is not connected at the time of OS install you will
wind up with duplicate labels when you connect the other drive and that
always leads to boot problems unless your fstab and grub.conf have the
device names

>  Labels would be a lot more useful if more applications displayed
> both
>  device and label (and mount point). When df displays only labels and
>  fdisk displays only device names, I have to look up what parameters to
>  give which tool to print labels for devices, and hand-map between the
>  two.  
>   
e2label tells you what label is on the specified partition.

>  It would also be very nice if I could tell fstab which partitions
> are
>  critical, and which should be ignored if not present, rather than
>  causing fatal errors.  Currently I seem to only be able to do this if
>  I don't mind mounting all non-critical partitions manually after boot. 
AFAIK, the only fatal errors occur if / or some other mandatory
partition (such as (maybe) /var or /usr) fail to mount. Otherwise it
just fails to mount, posts an error in the log, and continues on using
the mount point without the mounted filesystem. 

you could script that easily by specifying noauto for those you consider
non-critical, then put mount lines for them in rc.local


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