Bug 1575850

util-linux-ng package owns mount and umount, so reassigning there. I believe this is expected behaviour, though - as you mentioned, /etc/mtab can differ from actual /proc/mounts ... but Karel can better comment on this.

It would be nice to have examples (copy & past).

Anyway, the umount uses "-t" only when umount all filesystems (--all), otherwise the option is silently ignored. (Well, umount.8 man page should be probably more explicit about -t and -a relation. Now it's in synopsis only.)

Seems like NOTABUG.

STEP 1- : on running mount command, output is
[root@localhost ~]# mount
/dev/mapper/VolGroup-lv_root on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
nfsd on /proc/fs/nfsd type nfsd (rw)
/dev/sda1 on /boot type ext4 (rw)
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-1 on /Test/PERF/NFS3/TEST-1536309067_1 type nfs (rw,nfsvers=3,hard,intr,addr=10.164.8.32)
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-2 on /Test/PERF/NFS3/TEST-1536309067_2 type nfs (rw,nfsvers=3,hard,intr,addr=10.164.8.32)
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-3 on /Test/PERF/NFS3/TEST-1536309067_3 type nfs (rw,nfsvers=3,hard,intr,addr=10.164.8.32)
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-4 on /Test/PERF/NFS3/TEST-1536309067_4 type nfs (rw,nfsvers=3,hard,intr,addr=10.164.8.32)
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-5 on /Test/PERF/NFS3/TEST-1536309067_5 type nfs (rw,nfsvers=3,hard,intr,addr=10.164.8.32)
[root@localhost ~]#

STEP-2 on checking /proc/mounts, output is :

[root@localhost ~]# cat /proc/mounts
rootfs / rootfs rw 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
devtmpfs /dev devtmpfs rw,relatime,size=1948328k,nr_inodes=487082,mode=755 0 0
devpts /dev/pts devpts rw,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /dev/shm tmpfs rw,relatime 0 0
/dev/mapper/VolGroup-lv_root / ext4 rw,relatime,barrier=1,data=ordered 0 0
/proc/bus/usb /proc/bus/usb usbfs rw,relatime 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
/etc/auto.misc /misc autofs rw,relatime,fd=7,pgrp=2172,timeout=300,minproto=5,maxproto=5,indirect 0 0
-hosts /net autofs rw,relatime,fd=13,pgrp=2172,timeout=300,minproto=5,maxproto=5,indirect 0 0
nfsd /proc/fs/nfsd nfsd rw,relatime 0 0
/dev/sda1 /boot ext4 rw,relatime,barrier=1,data=ordered 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-1 /Test/PERF/NFS3/TEST-1536309067_1 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-2 /Test/PERF/NFS3/TEST-1536309067_2 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-3 /Test/PERF/NFS3/TEST-1536309067_3 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-4 /Test/PERF/NFS3/TEST-1536309067_4 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-5 /Test/PERF/NFS3/TEST-1536309067_5 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
/Test/PERF/NFS3/TEST-1536309067_1/ /Test/PERF/NFS3/TEST-1536309067_1 safenetfs rw,relatime 0 0
/Test/PERF/NFS3/TEST-1536309067_5/ /Test/PERF/NFS3/TEST-1536309067_5 safenetfs rw,relatime 0 0
/Test/PERF/NFS3/TEST-1536309067_4/ /Test/PERF/NFS3/TEST-1536309067_4 safenetfs rw,relatime 0 0
/Test/PERF/NFS3/TEST-1536309067_2/ /Test/PERF/NFS3/TEST-1536309067_2 safenetfs rw,relatime 0 0
/Test/PERF/NFS3/TEST-1536309067_3/ /Test/PERF/NFS3/TEST-1536309067_3 safenetfs rw,relatime 0 0

STEP 3 : when umount path with -t option where filesystem type mentioned is nfs, status of /etc/mtab is:

[root@localhost ~]# umount -a -t nfs
[root@localhost ~]# mount
/dev/mapper/VolGroup-lv_root on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
nfsd on /proc/fs/nfsd type nfsd (rw)
/dev/sda1 on /boot type ext4 (rw)


STEP 4: status of /proc/mounts is :
[root@localhost ~]# cat /proc/mounts
rootfs / rootfs rw 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
devtmpfs /dev devtmpfs rw,relatime,size=1948328k,nr_inodes=487082,mode=755 0 0
devpts /dev/pts devpts rw,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /dev/shm tmpfs rw,relatime 0 0
/dev/mapper/VolGroup-lv_root / ext4 rw,relatime,barrier=1,data=ordered 0 0
/proc/bus/usb /proc/bus/usb usbfs rw,relatime 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
/etc/auto.misc /misc autofs rw,relatime,fd=7,pgrp=2172,timeout=300,minproto=5,maxproto=5,indirect 0 0
-hosts /net autofs rw,relatime,fd=13,pgrp=2172,timeout=300,minproto=5,maxproto=5,indirect 0 0
nfsd /proc/fs/nfsd nfsd rw,relatime 0 0
/dev/sda1 /boot ext4 rw,relatime,barrier=1,data=ordered 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-1 /Test/PERF/NFS3/TEST-1536309067_1 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-2 /Test/PERF/NFS3/TEST-1536309067_2 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-3 /Test/PERF/NFS3/TEST-1536309067_3 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-4 /Test/PERF/NFS3/TEST-1536309067_4 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0
10.164.8.32:/opt/PfTest/JenkinsTest-a98f29254a48-nfsv3-5 /Test/PERF/NFS3/TEST-1536309067_5 nfs rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.164.8.32,mountvers=3,mountport=38256,mountproto=udp,local_lock=none,addr=10.164.8.32 0 0

Issue: we cannot see any entry in mtab for base nfs mount, but /proc/mounts still hold the entries for nfs. now if we check /etc/mtab only then we should be able to again mount these paths on nfs,but because entries are present in /proc/mounts error is given:
[root@localhost ~]# mount -a
mount.nfs: /Test/PERF/NFS3/TEST-1536309067_1 is busy or already mounted
mount.nfs: /Test/PERF/NFS3/TEST-1536309067_2 is busy or already mounted
mount.nfs: /Test/PERF/NFS3/TEST-1536309067_3 is busy or already mounted
mount.nfs: /Test/PERF/NFS3/TEST-1536309067_4 is busy or already mounted
mount.nfs: /Test/PERF/NFS3/TEST-1536309067_5 is busy or already mounted

which creates problem,
P.S. : we are unable to make entry for later filesystem mounts (safenetfs) in mtab,as mtab gets corrupted when number of paths is high.

yes, as per synopsis umount checks entries in /etc/mtab only so it is successfully removing the entries from mtab,

but in reality path is still mounted as shown in /proc/mounts.

For umount (in RHEL-6 where is no the symlink) is reality mtab and nothing else, and I do not see another way.

You need to keep your mtab to match reality... 

Note that implement umount for your use-case means that it will be necessary to parse /etc/mtab, and then /proc/mount to verify mtab validity and to join records from mtab with kernel. Seems like pretty complicated for so unusual use-case.

Why you do not have "safenetfs" in your mtab?

(In reply to Karel Zak from comment #6)
> For umount (in RHEL-6 where is no the symlink) is reality mtab and nothing
> else, and I do not see another way.
> 
> You need to keep your mtab to match reality... 
> 
> Note that implement umount for your use-case means that it will be necessary
> to parse /etc/mtab, and then /proc/mount to verify mtab validity and to join
> records from mtab with kernel. Seems like pretty complicated for so unusual
> use-case.
> 
> Why you do not have "safenetfs" in your mtab?

 we are unable to make entry for later filesystem mounts (safenetfs) in /etc/mtab,as /etc/mtab gets corrupted when number of mounts is high and multiple IO operation are done on these mounted paths.

Also yes, symlink is present in  RHEL 7 for mtab and proc mounts(this must be a fix to some issue or a feature added) and not in rhel 6.

/etc/mtab is editable and can be corrupted by some applications.

If not a symlink in rhel 6, can't we have a graceful implementation to honour -t option and return error/warning/message to show discrepancies between /etc/mtab and /proc/mounts ?

All utils which modify /etc/mtab need to use proper locking, it sound like mistake that the file is corrupted...

I'm really not sure if we really want to implement a new feature (workaround?) to RHEL6.10 update. 

I guess the problem is system shutdown (as "umount -t -a" does not make sense for any other use-case), maybe it would be better to use any script to check the system mount table and mtab before the shutdown or copy /proc/mounts to /etc/mtab.

Closing as WONTFIX.

The problem does not exist on RHEL >= 7 and all the issue is mostly about wrong mtab maintenance by 3rd-party utils rather than a real umount issue.