banshee/linux-collection/linux/ssh/filesystems

Filesystems of a Linux, by SSH

Returns, for each mounted filesystem, the used space, the free space, the size, the used and free inodes, and whether it is mounted read-only. Memory and pseudo filesystems are left out. Six watches are offered, each one set on the probe.

What changed since version 1

Inodes are measured: a filesystem can be full with free space left, when its inodes run out.
The mount mode is read: an ext4 that meets an error remounts itself read-only, and read-only raises a critical.
The used space is the one df shows, used over used plus available, root's reserve excluded; version 1 divided by the whole size, which stayed about 5 % under on ext4.
Filesystems are left out by their type (from /proc/mounts), no longer by their device name: a tmpfs named run or shm is left out too, as are overlay, squashfs (snaps) and CD images.
A mount point holding blanks is supported, and a mount point shown twice is judged once.
A df that cannot read one mount (and exits with an error) no longer stops the collector: the other filesystems are still measured. Reading no filesystem at all stops it misconfigured.
size is new. used, full-soon, free and missing keep their ids, kinds and defaults: a probe upgraded from version 1 keeps its settings.

How it works

The collector runs three commands:

cat /proc/mounts, for the type and the mode (rw or ro) of each mount;
df -P -k, for the space, in KiB;
df -P -i, for the inodes.

A mount point shown twice (stacked mounts) is judged once. A filesystem of size zero (proc, sysfs, cgroup…) is left out, as are the types tmpfs, devtmpfs, ramfs, overlay, squashfs, iso9660, udf, efivarfs, fuse.lxcfs and fuse.gvfsd-fuse.
A filesystem that does not count inodes (btrfs, vfat) has no inode values.
Portable: /proc/mounts is written by the kernel the same way on Alpine, Debian and Fedora; -P, -k and -i are options of df in BusyBox as in GNU coreutils. Nothing is written on the target.

Prerequisites

an SSH account for monitoring, without write rights;
the fingerprint of the server's host key, set in protocol:ssh:fingerprint (not needed when the Security settings trust the first SSH fingerprint presented).

Outputs

Output	Unit	Per	Meaning
`used`	%	filesystem (its mount point)	used space
`free`	MiB	filesystem	space available
`size`	GiB	filesystem	size
`inodes-used`	%	filesystem	used inodes
`inodes-free`	—	filesystem	free inodes
`mode`	—	filesystem	`rw` or `ro`

Watches

Watch	Kind	Defaults	Checked
`used` Used space	above, on `used`	warning 80, critical 90	yes
`full-soon` Full within a week	above, on `used`	warning 99, trend 7 d	yes
`free` Little free space	below, on `free`	critical 1024	no
`inodes` Inodes running out	above, on `inodes-used`	warning 80, critical 90	yes
`read-only` Mounted read-only	state, on `mode`	critical `ro`	yes
`missing` Filesystem missing	missing, on `used`	no expected name	yes, raises once names are set

Limits

A df that does not know -i (a BusyBox built without it) stops the collector misconfigured.
A stale network mount can make df hang: the run then ends on the SSH timeout, unreachable.
In a mount point, a run of blanks is read as a single one.
A filesystem mounted read-only on purpose raises read-only: uncheck it, or leave it out of the selection.