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Anecdocte: our sysadmin set similar thing up (at 90%) at one of my boxes. but conflicting configuration of debian os also reserved 15% of capacity for OS, so sy

by jiri 9y ago

Anecdocte: our sysadmin set similar thing up (at 90%) at one of my boxes. but conflicting configuration of debian os also reserved 15% of capacity for OS, so system became completely unresponsive at 85% full disk, without emailing message about free space - 85% was for our purpose effectively 100% full disk. Still dont know what lesson I should learn from this story.

more-coffee 9y ago
Reserved capacity as in `sudo tune2fs <volume> | grep Reserved block count`? Those should already be excluded from available diskspace, so that is kind of interesting.
- jiri 9y ago
  I am not sure how he was getting free space for email warning, but in final state, running df showed plenty of space on disk, although writing to files signals "no disk space" error.
  - db48x 9y ago
    Reserved capacity is reserved for use by root, so when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available. Kinda useless these days, but was very useful back when you might have server daemons and a bunch of normal users with shell accounts on the same machine.
    - teddyh 9y ago
      Huh? I have never seen that behavior, and I can’t reproduce it as described. Did it ever work that way? Do you have any reference for this?
      - db48x 9y ago
        Well, there's man tune2fs: -m reserved-blocks-percentage Set the percentage of the filesystem which may only be allocated by privileged processes. Reserving some number of filesystem blocks for use by privi‐ leged processes is done to avoid filesystem fragmentation, and to allow system daemons, such as syslogd(8), to continue to function correctly after non- privileged processes are prevented from writing to the filesystem. Normally, the default percentage of reserved blocks is 5%. -g group Set the group which can use the reserved filesystem blocks. The group parameter can be a numerical gid or a group name. If a group name is given, it is converted to a numerical gid before it is stored in the superblock.
        teddyh 9y ago
        I meant this bit: > when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available. I have never seen that. I have only ever seen the “real” available space being shown by tune2fs, not df or anything similar, which have always shown the space available after subtracting the reserved space.

by jiri 9y ago

more-coffee 9y ago

Reserved capacity as in `sudo tune2fs <volume> | grep Reserved block count`? Those should already be excluded from available diskspace, so that is kind of interesting.

jiri 9y ago
I am not sure how he was getting free space for email warning, but in final state, running df showed plenty of space on disk, although writing to files signals "no disk space" error.
- db48x 9y ago
  Reserved capacity is reserved for use by root, so when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available. Kinda useless these days, but was very useful back when you might have server daemons and a bunch of normal users with shell accounts on the same machine.
  - teddyh 9y ago
    Huh? I have never seen that behavior, and I can’t reproduce it as described. Did it ever work that way? Do you have any reference for this?
    - db48x 9y ago
      Well, there's man tune2fs: -m reserved-blocks-percentage Set the percentage of the filesystem which may only be allocated by privileged processes. Reserving some number of filesystem blocks for use by privi‐ leged processes is done to avoid filesystem fragmentation, and to allow system daemons, such as syslogd(8), to continue to function correctly after non- privileged processes are prevented from writing to the filesystem. Normally, the default percentage of reserved blocks is 5%. -g group Set the group which can use the reserved filesystem blocks. The group parameter can be a numerical gid or a group name. If a group name is given, it is converted to a numerical gid before it is stored in the superblock.
      - teddyh 9y ago
        I meant this bit: > when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available. I have never seen that. I have only ever seen the “real” available space being shown by tune2fs, not df or anything similar, which have always shown the space available after subtracting the reserved space.