It will definitely be the only utility I recall that uses a numeral.

Utility names should include lowercase letters (the lower character classification) and digits only from the portable character set.

• https://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html
  • https://pubs.opengroup.org/onlinepubs/9699919799/utilities/m4.html
    • m is for macro processor. 3 is the version number. In the days of its creation, programs were given as short a name as possible to preserve memory and disk space as both were expensive and in short supply.
    • https://en.wikipedia.org/wiki/M4_(computer_language)
  • https://pubs.opengroup.org/onlinepubs/9699919799/utilities/fort77.html
  • https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html
    • It was difficult to achieve a satisfactory solution to the problem of name space in option characters. When the standard developers desired to extend the historical cc utility to accept ISO C standard programs, they found that all of the portable alphabet was already in use by various vendors. Thus, they had to devise a new name, c89 (now superseded by c99), rather than something like cc -X.

Note that many versions of macOS adhere to these standards: https://www.opengroup.org/openbrand/register/ https://www.opengroup.org/openbrand/register/brand3700.htm https://www.opengroup.org/openbrand/register/brand3705.htm

I know it had been this way for decades and was grandfathered in as a feature

If people were more resistant to “grandfathered” features I think we would not have as much software as we do today: https://www.jwz.org/doc/worse-is-better.html https://en.wikipedia.org/wiki/Worse_is_better

provide about 50%–80% of what you want from an operating system

one expects that if the 50% functionality Unix and C support is satisfactory, they will start to appear everywhere.

Unix and C are the ultimate computer viruses.

users have already been conditioned to accept worse than the right thing.

It’s probably possible to make several programs with “50% functionality” in the time it takes to make one program with 100% functionality. Having more programs that are suitable for a majority of relevant applications is probably better than having one program that is suitable for all relevant applications, since having more programs will probably enable a larger variety of problems to be solved, and people often have to solve many different types of problems in their life.

what does usr mean

https://refspecs.linuxfoundation.org/fhs.shtml https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch04.html

Some operating systems may handle long path or file names in a surprising way, so having short paths and names is useful: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13

If any pathname component is longer than {NAME_MAX}, the implementation shall consider this an error.

if the combined length exceeds {PATH_MAX}, and the implementation considers this to be an error, pathname resolution shall fail

{NAME_MAX} and {PATH_MAX} are described in more detail at https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html#tag_13_23_03_02 and used in the context of https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pathchk.html

Note

The resources I linked are descriptive and not prescriptive, but in my experience they are suitable to depend upon as a reliable baseline, which makes meeting client requirements with software engineering easier.

You surely need to explicitly cause systemd to process changes after writing to a file. I would be very surprised if it reacted to file system changes automatically.

For example, I recall that I need to execute a command like systemctl daemon-reload after editing a service file: https://unix.stackexchange.com/questions/364782/what-does-systemctl-daemon-reload-do

You might get more useful information from resources like https://www.man7.org/linux/man-pages/man1/systemctl.1.html