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Viktor Joras
Asked: 2019-01-14 05:38:04 +0800 CST

Does Linux tmpfs filesystem need the sync option?

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I'm looking for info about mounting a tmpfs partition and sync option. Sync makes the data beeing dumped onto the disk without beeing saved in cache. This works with ext4 and other filesystems. I'm wondering is even a tmpfs partition needs the sync option to be specified or it is enabled by default since it is a RAM partition. In my option it would be odd if a ramdisk would be cached in RAM.

tmpfs /tmp tmpfs defaults,sync,noatime,nosuid,nodev,noexec,mode=0777,size=400M 0 0

In a tmpfs partition is sync enabled by default?

tmpfs

2 Answers

  1. Best Answer

    I had to search a bit. According to

    man mount

    The sync option is relevant only for a limited number of filesystems, not for tmpfs.

    So the answer is: It does not matter, since it is ignored by tmpfs.

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  2. Sync makes the data beeing dumped onto the disk without beeing saved in cache

    "Standard" Linux manual states:

       sync   All I/O to the filesystem should be done synchronously.
          In the case of media with a limited number of write cycles
          (e.g. some flash drives),  sync may cause life-cycle shortening.

    So it's not about cacheing but rather about durability. Writing synchronously doesn't mean there wouldn't be caching (for e. g., writethrough is well-known caching approach which is very different to writeback but both still are cacheing).

    In my option it would be odd if a ramdisk would be cached in RAM.

    As explained it doesn't prohibit cacheing but rather prohibits writeback-like behaviour. What would be odd is "durability" for RAM disk though.

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