What Happens When unrar Runs Out of Inodes?

Extracting an archive with unrar on a filesystem that has run out of inodes causes the extraction process to fail immediately when attempting to write new files or directories. Even if the disk has gigabytes of unallocated storage space remaining, the operating system cannot allocate metadata for new entries. Consequently, unrar throws file creation errors, halts or skips files, and leaves behind an incomplete extraction with non-zero exit status codes.

The Underlying System Error

In Unix-like filesystems (such as ext4, XFS, and UFS), an inode stores metadata about a file or directory, including permissions, ownership, and data block locations. Every file and folder consumes exactly one inode. When the filesystem reaches zero free inodes, the kernel cannot register new files.

When unrar attempts to unpack an entry, it issues system calls such as open() (with the O_CREAT flag) or mkdir(). Because no inodes are available, the kernel rejects these calls and returns the ENOSPC error code. Counterintuitively, the operating system translates ENOSPC as "No space left on device," which often misleads users into thinking they have exhausted raw disk storage capacity rather than inode entries.

How unrar Reacts

During execution, unrar encounters the kernel rejection and exhibits specific behaviors:

  • Error Messages: For every file it tries to unpack after inodes are exhausted, unrar prints an error directly to standard error or standard output: 
    Cannot create <filename>
No space left on device
  • Process Interruption: Depending on the exact flags used, unrar will either prompt the user for an action, skip the failing files, or terminate immediately.
  • Exit Codes: The utility terminates with a non-zero exit code (typically exit code 1 or 9 depending on the build and specific failure mode), indicating a fatal write failure to any calling scripts or processes.

State of the Filesystem After Failure

Running out of inodes during extraction leaves the filesystem in a messy, partial state:

  1. Incomplete Extraction: Any files processed before the inode exhaustion will remain intact on the filesystem. Any files queued after the limit was reached will be missing.
  2. Zero-Byte Files: In some edge cases, an inode might be allocated right as the limit is hit, but subsequent metadata or directory links cannot be established, leaving empty or truncated files.
  3. No Automatic Rollback: Standard unrar implementations do not provide transactional rollbacks. It will not clean up the files it successfully unpacked prior to the failure, requiring manual intervention to remove the partial data.

Identifying and Resolving the Issue

If an extraction fails with disk space errors when storage appears available, check inode consumption with the following command:

df -i

Look at the IUse% column for the target partition. If it shows 100%, the filesystem has no remaining inodes.

To resolve the issue and allow unrar to complete:

  • Delete large numbers of small, unused files, such as stale cache directories, old session files, or massive temporary log files.
  • Move the archive to another filesystem or a dynamic-inode filesystem (such as Btrfs or ZFS) that does not impose fixed inode limits.
  • Re-run the unrar command once free inodes appear in the df -i output.