o-append · shipping · also append mode

O_APPEND

O_APPEND is a file-status flag that combines positioning at the current end of a file with each write as one atomic operation.

Related Observatory article: O_APPEND on hesela.com

The status flag belongs to the open file description, so duplicated descriptors share it. Linux documents races when concurrent append is simulated on NFS; do not transfer a local-file guarantee to every network mount. [1] RWF_APPEND requests append for one pwritev2 operation; its supplied offset does not select the write position, while offset -1 also updates the current offset. [2]

Relations

related

pwrite, short-write, open-file-description, o-sync, advisory-file-lock

Advantages

• Avoids a separate seek-to-end followed by write for an append operation.

Limitations

• Does not make a multi-call record indivisible or request durable completion.
• Short writes still require byte-count accounting and a concurrency policy.

Citations

1. Linux man-pages 6.19: open(2), O_APPEND and open file descriptions (accessed 2026-10-17)
2. Linux man-pages 6.19: readv(2), RWF_APPEND and RWF_NOAPPEND (accessed 2026-10-17)

Further reading

3. Linux man-pages 6.19: write(2), partial writes and errors (accessed 2026-10-17)
4. Hesela: Atomic rename is not a durable commit (accessed 2026-10-17)

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