What is "C sort order" in pm-action manpage? [duplicate]

Question

From manpage pm-action(8):

/etc/pm/sleep.d, /usr/lib/pm-utils/sleep.d

Programs in these directories (called hooks) are combined and executed in C sort order before suspend and hibernate with as argument ´suspend´ or ´hibernate´.

Afterwards they are called in reverse order with argument ´resume´ and ´thaw´ respectively.

If both directories contain a similar named file, the one in /etc/pm/sleep.d will get preference. It is possible to disable a hook in the distribution directory by putting a non-executable file in /etc/pm/sleep.d, or by adding it to the HOOK_BLACKLIST configuration variable.

What is "C sort order"?

Does "a similar named file" mean two files with the same filename?

I have two files /usr/lib/pm-utils/sleep.d/94cpufreq and /etc/pm/sleep.d/20_cpu_freq. When resume and thaw, which one is run first and which second?

Thanks.

Answer 1

The C lexical sort order is very simple: characters with a lower numeric value sort before characters with a higher one. As almost all UNIX-derived systems nowadays use extended ASCII-derived character sets, the ordering would therefore be 8-bit as follows:

• Control characters: NUL-US (^@-^_: 0-26)
• Printable characters: (space)-/, 0-9, :-@, A-Z, [-` , a-z, {-~
• Extended characters: stuff afterwards (depends on the codepage)

Because of this, here are some filenames, in order:

!afile
0Afile
0_file
0afile
0~file
20-cpu_freq
20_cpu_freq
94Cpufreq
94cpufreq

By "similar named file", the two directory lists are combined, and if two file have the same name, the one in /etc/pm/sleep.d wins: if you had /usr/lib/pm-utils/sleep.d/94cpufreq and /etc/pm/sleep.d/94cpufreq, the latter would be read.

The order which these will be run is dictated by the operation that pm-utils is doing (from HOWTO.hooks):

SLEEP.D SPECIFIC NOTES

For any given sleep/wakeup cycle, the hooks in sleep.d are run twice:

• Once in C lexical sort order before the system goes to sleep, and
• Once in reverse C lexical sort order when the system wakes up.

TL;DR: 20_cpu_freq will be run first and 94cpufreq second when preparing to sleep, and the other way around when waking up.