Mounting
Notes for mounting filesystems on Linux/RHEL systems.
Use this page when checking mounted filesystems, mounting a disk, troubleshooting /etc/fstab, or investigating why a mount is missing after reboot.
Safety rule
Before mounting or unmounting anything, check:
1. Am I on the correct server?
2. Is this production or test?
3. What filesystem or mount point is affected?
4. Is the mount used by an application, database, or cluster?
5. Is this a local disk, SAN disk, NFS mount, or cluster-managed mount?
6. Is Veritas or another cluster tool managing this mount?
7. Do I have approval to unmount or remount?
Do not manually mount or unmount filesystems that are controlled by Veritas or another cluster manager unless you know the correct procedure.
Basic mount checks
Show mounted filesystems
mount
Cleaner view:
findmnt
Show one mount point
findmnt /mount/point
Example:
findmnt /data
Show disk usage
df -h
Show filesystem type too:
df -Th
Show block devices
lsblk
With filesystem information:
lsblk -f
Show filesystem UUIDs
blkid
Check /etc/fstab
/etc/fstab controls filesystems that should mount automatically.
View fstab
cat /etc/fstab
Example fstab line
UUID=xxxx-xxxx /data xfs defaults 0 0
Fields:
device/UUID mountpoint filesystem options dump fsck
Example with generic values:
UUID=1111-2222 /data xfs defaults 0 0
Mount from fstab
If the filesystem is already configured in /etc/fstab:
sudo mount /mount/point
Example:
sudo mount /data
Mount all fstab entries
sudo mount -a
Use carefully. This tests /etc/fstab without rebooting.
If /etc/fstab has a bad entry, it may show an error.
Manually mount a device
Basic syntax:
sudo mount /dev/DEVICE /mount/point
Example:
sudo mount /dev/sdb1 /data
Create a mount point
sudo mkdir -p /mount/point
Example:
sudo mkdir -p /data
Unmount a filesystem
sudo umount /mount/point
Example:
sudo umount /data
If unmount says "target is busy"
Check what is using the mount:
sudo lsof +f -- /mount/point
Alternative:
sudo fuser -vm /mount/point
Example:
sudo fuser -vm /data
Do not kill processes unless you understand the impact.
Remount a filesystem
Example: remount read-only:
sudo mount -o remount,ro /mount/point
Example: remount read-write:
sudo mount -o remount,rw /mount/point
Use carefully, especially on production systems.
NFS mounts
Show NFS mounts
mount | grep nfs
or:
findmnt -t nfs,nfs4
Mount an NFS share manually
sudo mount -t nfs NFS_SERVER:/export/path /mount/point
Example:
sudo mount -t nfs server01:/exports/data /mnt/data
Example NFS fstab line
server01:/exports/data /mnt/data nfs defaults 0 0
Check if mount is controlled by cluster
Before manually changing mounts, check if this server is clustered.
Possible Veritas checks:
hastatus -sum
hagrp -state
hares -state
If the mount belongs to a Veritas service group, do not manually mount/unmount unless you know the approved process.
Common mount problems
Mount point does not exist
Error may look like:
mount: mount point /data does not exist
Fix:
sudo mkdir -p /data
Then retry:
sudo mount /data
Filesystem type wrong
Check filesystem type:
lsblk -f
blkid
df -Th
Then verify /etc/fstab.
UUID wrong in fstab
Check real UUID:
blkid
Compare with:
cat /etc/fstab
Filesystem did not mount after reboot
Check:
findmnt /mount/point
df -h
systemctl --failed
journalctl -b -p err
cat /etc/fstab
Then test:
sudo mount -a
First command set for mount issues
hostnamectl
df -h
df -Th
findmnt
lsblk
lsblk -f
blkid
cat /etc/fstab
systemctl --failed
journalctl -b -p err
Dangerous actions
Be careful with:
umount on production filesystems
mount -o remount,rw
editing /etc/fstab
mount -a on production
mkfs
wipefs
fdisk
parted
changing cluster-managed mounts
These can break applications, databases, or boot.
Personal notes
Add sanitized notes here.
Examples:
- Mount was missing after reboot because fstab UUID was wrong.
- Mount point did not exist.
- NFS server was unreachable.
- Filesystem was controlled by Veritas, so manual mount was not safe.