bash – How to Clear Bash’s Cache of Paths to Executables

tl;dr

Running ssh 127.0.0.1 ydisplay sources ~/.bashrc rather than /etc/profile. Change your path in ~/.bashrc instead.

details

The only time /etc/profile is read is when your shell is a "login shell".

From the Bash Reference Manual:

When bash is invoked as a login shell, ... it first reads and executes commands from the file /etc/profile

But when you run ssh 127.0.0.1 ydisplay, bash is not started as a login shell. Yet it does read a different startup file. The Bash Reference Manual says:

when ... executed by ... sshd. ... it reads and executes commands from ~/.bashrc

So you should put your PATH settings in ~/.bashrc.

On most systems, ~/.bash_profile sources ~/.bashrc, so you can put your settings only in ~/.bashrc rather than putting them in both files.

There's no standard way to change the setting for all users, but most systems have a /etc/bashrc, /etc/bash.bashrc, or similar.

Failing that, set up pam_env and put the PATH setting in /etc/environment.

See also:

• What's the conf file reading between login and non-login shell?
• Is there a ".bashrc" equivalent file read by all shells?

Highest priority is bash alias, then special builtins (only in POSIX mode), then functions, then builtins, then a search in $PATH.

To execute a builtin, use builtin test.
To execute an external application, use an explicit path: /bin/test.
To ignore functions and aliases, use command test.
To bypass just alias, use \test or any other kind of expansion.

It's possible to disable/enable a builtin with enable test.

(Updated according to comments below)
(Fixed incorrect admin edit that bash has disable builtin - in fact, there is only enable)