ENOSPC

ENOSPC, short for "No space left on device," is an error code used by Unix-like operating systems to indicate that a write or allocation operation cannot proceed because there is no available space on the target filesystem. It is defined as errno 28 in POSIX systems and is typically reported by system calls such as write, fsync, or similar file- and block-level operations.

Causes of ENOSPC include a completely full data area of the filesystem, exhaustion of inodes (the metadata structures that track files), or quotas that restrict further allocation for a user or group. Some filesystems also reserve a portion of space for the root user to perform maintenance; if that reserved space is exhausted, non-root users may encounter ENOSPC even when some space remains visible to root.

When ENOSPC is returned, applications may fail to write new data, and logs or temporary files may fail to be created. Users might notice system utilities reporting full disks or inode usage while free space seems limited or inodes appear exhausted.

Diagnosis commonly involves:

- Checking available space with df -h and inode usage with df -i.

- Reviewing quotas with quota or repquota.

- Inspecting for unexpectedly large files, old logs, or caches that can be cleaned.

- Verifying whether reserved blocks are consuming space on certain filesystems (e.g., ext4) and whether adjustments are appropriate.

Mitigation strategies include freeing space (deleting or archiving files, truncating logs), removing unnecessary caches, rotating logs, or moving data to larger storage. If inodes are exhausted, removing small files or increasing the number of inodes during filesystem creation may be necessary. In some cases, resizing or repurposing the filesystem or adjusting reserved-block settings with appropriate tooling is required.