A no-space error belongs to the filesystem receiving the write, which may differ from the disk shown in a desktop summary. Some Linux filesystems can also run out of file metadata entries, called inodes, while still showing free storage blocks. Measure both before deleting a large document at random.

Measure the destination

Record the exact location where the application tried to save. In a terminal, run df -h followed by that existing directory's quoted path. This reports space for the filesystem containing the path. Compare the filesystem and mount location with the destination you intended.

Run df -i for the same path to inspect inode information. On filesystems that report these values, high inode use with little available capacity can explain why creating another small file fails. Deleting one large file may release many blocks while scarcely changing the number of available inodes.

Keep both readings with the original error. A healthy value in both does not rule out other limits, such as a quota or an application writing temporary data to a different location. Avoid turning one measurement into a universal diagnosis.

Find the responsible data class

If inode pressure is the clue, investigate directories containing very large numbers of small files. GNU du supports inode reporting and limiting traversal to one filesystem. Ask an administrator to scope that inspection to the affected filesystem so that mounted drives are not mixed into the comparison.

Identify what creates the files before cleaning them. A cache may have a supported cleanup method; an application database or job queue may not tolerate manual deletion. Preserve business records and establish whether a runaway process would immediately recreate the problem.

After an authorised cleanup, repeat both measurements and create, save and reopen a harmless file in the original destination. Record the result using the original application too. The acceptance check is renewed ability to perform the failed write, supported by the relevant filesystem capacity change.

Sources: Ubuntu documentation, Ubuntu documentation.