Error "manpath list too long" with man v2.6.3 MANPATH exceeds 50 directories

[tardigradus]

On CentOS 7.9, the version of 'man' is 2.6.3. This version seems to have a limit of 50 directories for MANPATH. If this is exceeded, which sometimes happens with EasyBuild, 'man' will produce the error

man: manpath list too long

Versions 2.9.3 (AlmaLinux 9.1) and 2.9.4 (Debian 11) don't have this limitation (or the limit is higher).

Workaround from Steen Lysgaard:

Doing

unset MANPATH

after loading many Easybuild modules allows still allows manpages to
be found for any program that has the manpages relative to the
executable like this: ../share/man.

Suggested solution from Alan O'Cais:

Add some functionality to eb to only set MANPATH if the above structure is not respected.

[akesandgren]

There is no mention of that behaviour, looking for manpages in ../share/man, in the man-page for man, so that needs to be verified for any OS release we might be running on before such a change is made.

[zao]

I assume that this is some sort of fallback heuristic.

What happens if you request a page that is present in a system location or earlier in the MANPATH but is for a different version of the program than you expected?
For example, if you man gcc, would it get you the page for the system compiler or the implicit one adjacent to the software from a module?

[tardigradus]

If I run

MANPAGE= man gcc

I get the page for version 4.8.5, which is the system version on my system. If I run

module add GCCcore/11.3.0
MANPAGE= man gcc

I get the page for version 11.3.0. The order in PATH seems to be the determining factor.