kovidgoyal/kitty · warning

Failed to allocate space for new disk cache file during defr

Error message

Failed to allocate space for new disk cache file during defrag

What it means

During disk-cache defrag, ftruncate() on the newly opened cache file failed, so kitty could not pre-allocate space for the compacted entries. Almost always ENOSPC — the filesystem holding the cache cannot fit total_data_size bytes. Defrag aborts cleanly; data remains in the old file.

Source

Thrown at kitty/disk-cache.c:246

    defrag_entries = calloc(num_entries, sizeof(DefragEntry));
    if (!defrag_entries) goto cleanup;
    size_t total_data_size = 0, num_entries_to_defrag = 0;
    cache_map_for_loop(i) {
        CacheValue *s = i.data->val;
        if (s->pos_in_cache_file > -1 && s->data_sz) {
            total_data_size += s->data_sz;
            DefragEntry *e = defrag_entries + num_entries_to_defrag++;
            e->old_offset = s->pos_in_cache_file;
            e->data_sz = s->data_sz;
            e->key = keydup(i.data->key); // have to dup the key as we release the mutex and another thread might free the underlying key.
            if (!e->key.hash_key) {
                fprintf(stderr, "Failed to allocate space for keydup in defrag\n");
                goto cleanup;
            }
        }
    }
    if (ftruncate(new_cache_file, total_data_size) != 0) {
        perror("Failed to allocate space for new disk cache file during defrag");
        goto cleanup;
    }
    lseek(new_cache_file, 0, SEEK_SET);

    mutex(unlock);
    lock_released = true;

    off_t current_pos = 0;
    for (size_t i = 0; i < num_entries_to_defrag; i++) {
        DefragEntry *e = defrag_entries + i;
        if (!copy_between_files(self->cache_file_fd, new_cache_file, e->old_offset, e->data_sz, &fcb)) {
            perror("Failed to copy data to new disk cache file during defrag");
            goto cleanup;
        }
        e->new_offset = current_pos;
        current_pos += e->data_sz;
    }
    ok = true;

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Free space on the filesystem containing the cache dir or move XDG_CACHE_HOME to a larger volume.
2. Clear the old cache: quit kitty and delete the kitty disk-cache directory.
3. Reduce scrollback size in kitty.conf to shrink total_data_size.
4. Avoid putting the cache on FUSE/NFS mounts; keep it on a local fs.

df -h "${XDG_CACHE_HOME:-$HOME/.cache}"  # confirm free bytes > expected scrollback cache size

When it happens

Trigger: defrag() runs (triggered from find_cache_entry_to_write once fragmentation thresholds are met) and the sum of live entry sizes exceeds free space on the cache filesystem, or the fs doesn't support ftruncate (some FUSE/network mounts return EPERM/EINVAL).

Common situations: Large scrollback caches on a small tmpfs; cache dir on a full home partition; cache on a network filesystem (NFS) with locking/truncate quirks.

Related errors

• Failed to open second file for defrag of disk cache
• Failed to write to disk-cache file
• Failed to copy data to new disk cache file during defrag
• Failed to seek in disk cache file
• This must be run as kitten ask

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/6cd883cfe3496400. Report an issue: GitHub.