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Re^5: Preventing multiple instances

by afoken (Canon)
on Dec 18, 2020 at 16:33 UTC ( #11125414=note: print w/replies, xml ) Need Help??

in reply to Re^4: Preventing multiple instances
in thread Preventing multiple instances

Can you explain why you chose /var/memdir and not /tmp/memdir as it is by its very nature temporary.

I'm guessing this is a design decision, not something that is going to be explained in the documentation.

/tmp is often already on a ramdisk-like virtual filesystem, e.g. tmpfs. If not, some boot script cleans up tmp. So /tmp/memdir is gone after a reboot. /var is on persistent storage, so /var/memdir will survive a reboot.

Also, any reason to set the number of blocks to zero?

This documentation doesn't cover the size=1M 0 0 parameter and I cannot find reference to it in the links. I asked because when I looked up what these parameters do I found advice that "It is generally unwise to mount with such options" in this article.

/etc/fstab is structured, six fields separated by whitespace. This implies that no field can contain whitespace. The fields are (in order):

  1. fs_spec (roughly the device to be mounted)
  2. fs_file (the mount point)
  3. fs_vfstype (filesystem type
  4. fs_mntops (mount options for the filesystem)
  5. fs_freq ("This field is used by dump(8) to determine which filesystems need to be dumped. Defaults to zero (don't dump) if not present.")
  6. fs_passno (used to select the order for fsck at boot. / should have 1, others 2, 0 disables fsck at boot)

"size=1M" is part of the mount options in field 4, the two zeros after that are fields 5 and 6.

stevieb proposed to add this to fstab:

tmpfs /var/memdir tmpfs nodev,nosuid,size=1M 0 0

Split at whitespace and compare with the field descriptions.


Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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