make: Options/Recursion
5.7.3 Communicating Options to a Sub-'make'
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Flags such as '-s' and '-k' are passed automatically to the sub-'make'
through the variable 'MAKEFLAGS'. This variable is set up automatically
by 'make' to contain the flag letters that 'make' received. Thus, if
you do 'make -ks' then 'MAKEFLAGS' gets the value 'ks'.
As a consequence, every sub-'make' gets a value for 'MAKEFLAGS' in
its environment. In response, it takes the flags from that value and
processes them as if they had been given as arguments. 
Summary of
Options Options Summary.
Likewise variables defined on the command line are passed to the
sub-'make' through 'MAKEFLAGS'. Words in the value of 'MAKEFLAGS' that
contain '=', 'make' treats as variable definitions just as if they
appeared on the command line. Overriding Variables Overriding.
The options '-C', '-f', '-o', and '-W' are not put into 'MAKEFLAGS';
these options are not passed down.
The '-j' option is a special case (Parallel Execution
Parallel.). If you set it to some numeric value 'N' and your operating
system supports it (most any UNIX system will; others typically won't),
the parent 'make' and all the sub-'make's will communicate to ensure
that there are only 'N' jobs running at the same time between them all.
Note that any job that is marked recursive (Instead of Executing
Recipes Instead of Execution.) doesn't count against the total jobs
(otherwise we could get 'N' sub-'make's running and have no slots left
over for any real work!)
If your operating system doesn't support the above communication,
then no '-j' is added to 'MAKEFLAGS', so that sub-'make's run in
non-parallel mode. If the '-j' option were passed down to sub-'make's
you would get many more jobs running in parallel than you asked for. If
you give '-j' with no numeric argument, meaning to run as many jobs as
possible in parallel, this is passed down, since multiple infinities are
no more than one.
If you do not want to pass the other flags down, you must change the
value of 'MAKEFLAGS', like this:
subsystem:
cd subdir && $(MAKE) MAKEFLAGS=
The command line variable definitions really appear in the variable
'MAKEOVERRIDES', and 'MAKEFLAGS' contains a reference to this variable.
If you do want to pass flags down normally, but don't want to pass down
the command line variable definitions, you can reset 'MAKEOVERRIDES' to
empty, like this:
MAKEOVERRIDES =
This is not usually useful to do. However, some systems have a small
fixed limit on the size of the environment, and putting so much
information into the value of 'MAKEFLAGS' can exceed it. If you see the
error message 'Arg list too long', this may be the problem. (For strict
compliance with POSIX.2, changing 'MAKEOVERRIDES' does not affect
'MAKEFLAGS' if the special target '.POSIX' appears in the makefile. You
probably do not care about this.)
A similar variable 'MFLAGS' exists also, for historical
compatibility. It has the same value as 'MAKEFLAGS' except that it does
not contain the command line variable definitions, and it always begins
with a hyphen unless it is empty ('MAKEFLAGS' begins with a hyphen only
when it begins with an option that has no single-letter version, such as
'--warn-undefined-variables'). 'MFLAGS' was traditionally used
explicitly in the recursive 'make' command, like this:
subsystem:
cd subdir && $(MAKE) $(MFLAGS)
but now 'MAKEFLAGS' makes this usage redundant. If you want your
makefiles to be compatible with old 'make' programs, use this technique;
it will work fine with more modern 'make' versions too.
The 'MAKEFLAGS' variable can also be useful if you want to have
certain options, such as '-k' (Summary of Options Options
Summary.), set each time you run 'make'. You simply put a value for
'MAKEFLAGS' in your environment. You can also set 'MAKEFLAGS' in a
makefile, to specify additional flags that should also be in effect for
that makefile. (Note that you cannot use 'MFLAGS' this way. That
variable is set only for compatibility; 'make' does not interpret a
value you set for it in any way.)
When 'make' interprets the value of 'MAKEFLAGS' (either from the
environment or from a makefile), it first prepends a hyphen if the value
does not already begin with one. Then it chops the value into words
separated by blanks, and parses these words as if they were options
given on the command line (except that '-C', '-f', '-h', '-o', '-W', and
their long-named versions are ignored; and there is no error for an
invalid option).
If you do put 'MAKEFLAGS' in your environment, you should be sure not
to include any options that will drastically affect the actions of
'make' and undermine the purpose of makefiles and of 'make' itself. For
instance, the '-t', '-n', and '-q' options, if put in one of these
variables, could have disastrous consequences and would certainly have
at least surprising and probably annoying effects.
If you'd like to run other implementations of 'make' in addition to
GNU 'make', and hence do not want to add GNU 'make'-specific flags to
the 'MAKEFLAGS' variable, you can add them to the 'GNUMAKEFLAGS'
variable instead. This variable is parsed just before 'MAKEFLAGS', in
the same way as 'MAKEFLAGS'. When 'make' constructs 'MAKEFLAGS' to pass
to a recursive 'make' it will include all flags, even those taken from
'GNUMAKEFLAGS'. As a result, after parsing 'GNUMAKEFLAGS' GNU 'make'
sets this variable to the empty string to avoid duplicating flags during
recursion.
It's best to use 'GNUMAKEFLAGS' only with flags which won't
materially change the behavior of your makefiles. If your makefiles
require GNU make anyway then simply use 'MAKEFLAGS'. Flags such as
'--no-print-directory' or '--output-sync' may be appropriate for
'GNUMAKEFLAGS'.
Info Catalog
make: Variables/Recursion
make: Recursion
make: -w Option