Writhing this in case somebody finds it helpful. tl;dr: filesystem crashed due to overfilling, refused to mount with errno -5, was recovered automatically by nilfs-resize Due do my mix-up I have over-filled my root filesystem (220GB) with large file (~150GB), as root. The filesystem locked up (kernel 5.14.0-rc6), after forced restart refused to mount, returning errno -5. The nilfs-tune tool indicated seemingly correct content. other tools could not access the filesystem. Under pressure of time I have given up on it and decided to re-install system; using nilfs-resize (through gparted) unexpectedly recovered the filesystem. The tool correctly detected filesystem and was able to work with it, but for completion required a number of extra blocks to perform the operation. The filesystem worked since. Again, due to time pressure I wasn't able to preserve filesystem snapshot or anything - only this written summary is available. Best regards, -- dexen
