[wpollock]

Why would strace cat be useful here? By the time cat runs, it was obviously already found.

It is basic knowledge that PATH is used by a command interpreter to locate the pathname of binaries. This is true for Window's cmd.exe as well. I never heard of a system where locating files for execution was performed by a kernel.

[V99]

True... `strace bash -c cat` would give more the series of stat calls they're intending to see:

newfstatat(AT_FDCWD, ".", {st_mode=S_IFDIR|0700, st_size=4096, ...}, 0) = 0

newfstatat(AT_FDCWD, "/usr/local/sbin/cat", 0x7fffcec2f3b8, 0) = -1 ENOENT (No such file or directory)

newfstatat(AT_FDCWD, "/usr/local/bin/cat", 0x7fffcec2f3b8, 0) = -1 ENOENT (No such file or directory)

newfstatat(AT_FDCWD, "/usr/sbin/cat", 0x7fffcec2f3b8, 0) = -1 ENOENT (No such file or directory)

newfstatat(AT_FDCWD, "/usr/bin/cat", {st_mode=S_IFREG|0755, st_size=68536, ...}, 0) = 0

[userbinator]

I never heard of a system where locating files for execution was performed by a kernel.

Also true for MS/PC-DOS... which also holds the distinction of having some rare "truly monolithic" API-compatible variants that put the kernel, drivers, and shell in a single binary, so that may satisfy your criteria.

[MathMonkeyMan]

In the [exec][1] family of POSIX functions, if the command path doesn't contain a slash, then it's looked up in the PATH.

> If the file argument contains a slash character, the file argument shall be used as the pathname for this file. Otherwise, the path prefix for this file is obtained by a search of the directories passed as the environment variable PATH [...]

[1]: https://pubs.opengroup.org/onlinepubs/009695399/functions/ex...

[yencabulator]

Those are just functions in a library, not seen by strace which is about syscalls.

[HelloNurse]

The kernel's job is to execute executable files, while the shell's job is to bridge the gap between a user-facing command name ("cat") and an executable file (/usr/bin/cat). The PATH environment variable provides such a good general and transparent way to control this task that most shells on most operating systems work that way.