Here are the names for the POSIX minimum upper bounds for the system limit parameters. The significance of these values is that you can safely push to these limits without checking whether the particular system you are using can go that far.
_POSIX_AIO_LISTIO_MAX ¶The most restrictive limit permitted by POSIX for the maximum number of
I/O operations that can be specified in a list I/O call. The value of
this constant is 2; thus you can add up to two new entries
of the list of outstanding operations.
_POSIX_AIO_MAX ¶The most restrictive limit permitted by POSIX for the maximum number of
outstanding asynchronous I/O operations. The value of this constant is
1. So you cannot expect that you can issue more than one
operation and immediately continue with the normal work, receiving the
notifications asynchronously.
_POSIX_ARG_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum combined length of the argv and environ
arguments that can be passed to the exec functions.
Its value is 4096.
_POSIX_CHILD_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of simultaneous processes per real user ID. Its
value is 6.
_POSIX_NGROUPS_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of supplementary group IDs per process. Its
value is 0.
_POSIX_OPEN_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of files that a single process can have open
simultaneously. Its value is 16.
_POSIX_SSIZE_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum value that can be stored in an object of type
ssize_t. Its value is 32767.
_POSIX_STREAM_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum number of streams that a single process can have open
simultaneously. Its value is 8.
_POSIX_TZNAME_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the maximum length of a time zone abbreviation. Its value is 3.
_POSIX2_RE_DUP_MAX ¶The value of this macro is the most restrictive limit permitted by POSIX
for the numbers used in the ‘\{min,max\}’ construct
in a regular expression. Its value is 255.