Error opening file: Permission denied – backup creation failure in nano

Answer the question first

When nano is started with -B (or --backup) and it cannot create the backup file, it exits with Error opening file: Permission denied. Nano’s design is to avoid writing a file that has no backup, which could leave the file in an inconsistent state.

Likely explanation

• The backup file file~ is created in the same directory as the target file.
• If the user lacks write permission on that directory, the open(2) call fails with EACCES, and nano aborts.

Confirmed facts

• The error originates from the backup routine, not from opening the target file itself.
• The abort is intentional in current nano releases (≥5.9). The manual mentions the backup file but does not describe the abort explicitly.

Practical steps for this case

1. ls -l /path/to/file and ls -ld $(dirname /path/to/file) to check ownership and write permission on the directory.
2. If you lack write permission, either:
   • Run sudo nano /path/to/file (be careful to restore original ownership after editing).
   • Move the file to a writable directory, edit it, then copy it back.
   • Or, if you cannot change permissions, launch nano without -b or disable backups in ~/.nanorc with set backup 0.
3. After editing, verify that the target file was updated with ls -l and that a backup file file~ exists if backups were enabled.

Does the manual describe this behavior?

The --backup description in man nano states that a backup file named file~ is created in the same directory. It does not mention the abort, but the source code shows the abort is intentional to protect against writing a file without a backup.

Missing diagnostic detail

Is the file located in a system directory such as /etc or a user‑writable location? Knowing the directory context helps decide whether sudo is appropriate or a permission tweak suffices.