01-11-2018
Hi,
Taking your questions in turn:
1. Buffers and cache are essentially types of memory that, whilst they are in use, could be freed up if the system required memory for some other purpose. These are types of memory that are mostly used to hold things which either are yet to be written or have recently been read from disk, in order to accelerate file I/O. So if ever a process genuinely needs more memory than is sitting absolutely unused (which is the total in the 'free' column) more can be obtained by flushing out certain things from the buffers and/or cache.
2. The 'free' column shows you the memory on the system which is genuinely 100% unused - so not in use by a process, and not part of the buffers, cache or shared memory pool. The 'available' column consists of the 'free' memory, plus whatever memory from other categories (mainly the buffers and cache) which could be easily freed up if required. So you can take 'available' as a trustworthy figure as the amount of free memory that applications could use if they needed to.
Hope this helps.
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LEARN ABOUT SUNOS
systemd-cryptsetup-generator
SYSTEMD-CRYPTSETUP-GENERATOR(8) systemd-cryptsetup-generator SYSTEMD-CRYPTSETUP-GENERATOR(8)
NAME
systemd-cryptsetup-generator - Unit generator for /etc/crypttab
SYNOPSIS
/lib/systemd/system-generators/systemd-cryptsetup-generator
DESCRIPTION
systemd-cryptsetup-generator is a generator that translates /etc/crypttab into native systemd units early at boot and when configuration of
the system manager is reloaded. This will create systemd-cryptsetup@.service(8) units as necessary.
systemd-cryptsetup-generator implements systemd.generator(7).
KERNEL COMMAND LINE
systemd-cryptsetup-generator understands the following kernel command line parameters:
luks=, rd.luks=
Takes a boolean argument. Defaults to "yes". If "no", disables the generator entirely. rd.luks= is honored only by initial RAM disk
(initrd) while luks= is honored by both the main system and the initrd.
luks.crypttab=, rd.luks.crypttab=
Takes a boolean argument. Defaults to "yes". If "no", causes the generator to ignore any devices configured in /etc/crypttab
(luks.uuid= will still work however). rd.luks.crypttab= is honored only by initial RAM disk (initrd) while luks.crypttab= is honored
by both the main system and the initrd.
luks.uuid=, rd.luks.uuid=
Takes a LUKS superblock UUID as argument. This will activate the specified device as part of the boot process as if it was listed in
/etc/crypttab. This option may be specified more than once in order to set up multiple devices. rd.luks.uuid= is honored only by
initial RAM disk (initrd) while luks.uuid= is honored by both the main system and the initrd.
If /etc/crypttab contains entries with the same UUID, then the name, keyfile and options specified there will be used. Otherwise, the
device will have the name "luks-UUID".
If /etc/crypttab exists, only those UUIDs specified on the kernel command line will be activated in the initrd or the real root.
luks.name=, rd.luks.name=
Takes a LUKS super block UUID followed by an "=" and a name. This implies rd.luks.uuid= or luks.uuid= and will additionally make the
LUKS device given by the UUID appear under the provided name.
rd.luks.name= is honored only by initial RAM disk (initrd) while luks.name= is honored by both the main system and the initrd.
luks.options=, rd.luks.options=
Takes a LUKS super block UUID followed by an "=" and a string of options separated by commas as argument. This will override the
options for the given UUID.
If only a list of options, without an UUID, is specified, they apply to any UUIDs not specified elsewhere, and without an entry in
/etc/crypttab.
rd.luks.options= is honored only by initial RAM disk (initrd) while luks.options= is honored by both the main system and the initrd.
luks.key=, rd.luks.key=
Takes a password file name as argument or a LUKS super block UUID followed by a "=" and a password file name.
For those entries specified with rd.luks.uuid= or luks.uuid=, the password file will be set to the one specified by rd.luks.key= or
luks.key= of the corresponding UUID, or the password file that was specified without a UUID.
rd.luks.key= is honored only by initial RAM disk (initrd) while luks.key= is honored by both the main system and the initrd.
SEE ALSO
systemd(1), crypttab(5), systemd-cryptsetup@.service(8), cryptsetup(8), systemd-fstab-generator(8)
systemd 237 SYSTEMD-CRYPTSETUP-GENERATOR(8)