How to Diagnose and Fix Disk‑Full, Read‑Only, and Inode Issues on Linux

1. No space left on device

When a UNIX‑like system runs out of disk space, commands such as fallocate -l 1G test4.img fail with the error "No space left on device". Use df -h to view total and available space for each mounted filesystem.

# fallocate -l 1G test4.img
fallocate: test4.img: No space left on device
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda6       117G   54G   57G  49% /
... (other partitions) ...

Fixing a full disk

Compress logs or large files with gzip /ftpusers/tmp/*.log or bzip2 /ftpusers/tmp/large.file.name.

Delete unwanted files using rm -rf /ftpusers/tmp/*.bmp.

Move files to another system or external drive with

rsync --remove-source-files -azv /ftpusers/tmp/*.mov /mnt/usbdisk/

.

Find the biggest directories or files: du -a /ftpusers/tmp | sort -nr | head -n 10 or du -cks *.

Truncate large log files: truncate -s 0 /ftpusers/ftp.upload.log.

Identify and delete deleted but still open files using lsof -nP | grep '(deleted)' or find /proc/*/fd -ls | grep '(deleted)'.

2. Filesystem is read‑only

If creating or saving a file yields "Read‑only file system", check the mount options with mount. Remount the filesystem as read‑write:

# mount -o remount,rw /ftpusers/tmp

On FreeBSD, remount the root filesystem with mount -o rw /dev/ad0s1a /. If the read‑only state is caused by hardware failure, replace the drive instead of forcing a write‑able mount.

3. Running out of inodes

Even when df -h shows free space, the filesystem may be out of inodes. Check inode usage with df -i:

$ df -i /ftpusers
Filesystem      Inodes   IUsed   IFree IUse% Mounted on
/dev/sda8     6250496   11568 6238928    1% /ftpusers

If inode usage reaches 100%, delete unnecessary small files or combine them into larger archives, or repartition with a higher inode count.

4. Disk health monitoring

Use smartctl -a /dev/sda to view SMART data and detect hardware errors. The hddtemp utility can report drive temperature:

$ hddtemp /dev/sda
/dev/sda: 35°C

Example output from smartctl -d ata -A /dev/sda filtered for temperature:

# smartctl -d ata -A /dev/sda | grep -i temperature
...

CPU temperature

Install lm-sensors and run sensors to see CPU core temperatures.

5. Repairing a corrupted filesystem

Unmount the affected partition and run fsck -y /dev/sda8 to fix errors.

6. Managing Linux software RAID (mdadm)

Check RAID status with mdadm --detail /dev/md0 or cat /proc/mdstat. To replace a failed drive:

# mdadm --manage /dev/md0 --fail /dev/sdb1
# mdadm --manage /dev/md0 --remove /dev/sdb1
# sfdisk -d /dev/sda | sfdisk /dev/sdb
# mdadm --manage /dev/md0 --add /dev/sdb1

Monitor synchronization progress with watch cat /proc/mdstat.

7. Managing hardware RAID controllers

Use vendor‑specific tools such as smartctl -d scsi --all /dev/sgX, /usr/StorMan/arcconf getconfig 1, or tw_cli /c0 show to query and replace failed disks.

Conclusion

These tips help resolve common disk‑related problems on Linux/UNIX servers, from full filesystems and read‑only mounts to inode exhaustion and hardware failures. Implement regular backups and monitoring to recover from disk failures, accidental deletions, or catastrophic system loss.