Scheduling / descheduling linux host reboots via shutdown

Scheduling and/or descheduling linux host reboots is possible with the shutdown -r command using the time parameter (the reboot command, that I usually prefer in favour of clarity, does’nt feature the time parameter, so shutdown -r is the only choice here). Aside from discussing the quite straightforward man page of shutdown, there is two points here to register in your knowledge cells.
First, a (scheduled) shutdown -r hh24:mi execution will hangup itself into background, no need to use job-tools or an &. shutdown -r hh24:mi actually puts systemd-shutdownd in charge of serving the party, this is what you”ll want to expect to see in your running process list, looking for some command effect. Also, a running scheduled shutdown may be cancelled using shutdown -c any time before hh24:mi. Note however, that from around five minutes before hh24:mi, you’ll you’ll no longer be allowed to login the machine, essentially impeding any further control from your side.


Log-dedicated loop device throughput and time overhead on btrfs 4.x

This is again about real world numbers (which I like so much for being authentic ;-). The context being the throughput and time overhead of a loop device, as a poor or late man’s replacement for a real disk partition, jep I know, on copy-on-write filesystem btrfs, exclusively dedicated for logging, that is appending over and over. Why? The loop device may overflow with data without affecting the underlying filesystem, see Btrfs subvolume quota still in its infancy with btrfs version 4.2.2 for more why’s and what I tried to get btrfs subvolume with quota to work. By the way, about that though, see debian org Btrfs for a down-to-earth assessment of btrfs to date, even uttering a recommendation from what version number (4.4) to start off at the earliest near production. Anyway, what follows, adapts a test setup as in Performance of loopback filesystems, prime credits go there, and expands the layout somewhat for the btrfs C or nodatacow flag. Here we go.

Have this baseline, if you like, test on the raw iron. Well, its not raw iron really, its vmware and tons of storage below, and the shown performance is terrible I know and I only take one testset of bs / count but that won’t matter. There’s something to start off.

mkdir /tmp/loop0
dd if=/dev/zero bs=1M of=/tmp/loop0/file oflag=sync count=1000
1048576000 bytes (1.0 GB) copied, 8.9605 s, 117 MB/s
1048576000 bytes (1.0 GB) copied, 6.52867 s, 161 MB/s
1048576000 bytes (1.0 GB) copied, 5.35716 s, 196 MB/s
1048576000 bytes (1.0 GB) copied, 5.48745 s, 191 MB/s
1048576000 bytes (1.0 GB) copied, 5.14736 s, 204 MB/s