Error 2 after make install when installing gmp-4.2.4

[Krishna]

Dear Sir/madam,
                            I Krishna Prasad, When i try to install gmp-4.2.4 via terminal of Ubuntu 8.10 and follows the instruction given in document as follows:
                          ./configure
                           make
                           make check
                           make install
all these are in the directory were i have saved gmp-4-2.4. The problem occurs after make install as follows (last few line of terminal are):-
.
.
.
make[4]: Leaving directory `/home/krishna/Software/gmp-4.2.4/demos'
make[3]: Leaving directory `/home/krishna/Software/gmp-4.2.4/demos'
make[2]: Leaving directory `/home/krishna/Software/gmp-4.2.4/demos'
Making install in tune
make[2]: Entering directory `/home/krishna/Software/gmp-4.2.4/tune'
make[3]: Entering directory `/home/krishna/Software/gmp-4.2.4/tune'
make[3]: Nothing to be done for `install-exec-am'.
make[3]: Nothing to be done for `install-data-am'.
make[3]: Leaving directory `/home/krishna/Software/gmp-4.2.4/tune'
make[2]: Leaving directory `/home/krishna/Software/gmp-4.2.4/tune'
Making install in doc
make[2]: Entering directory `/home/krishna/Software/gmp-4.2.4/doc'
make[3]: Entering directory `/home/krishna/Software/gmp-4.2.4/doc'
make[3]: Nothing to be done for `install-exec-am'.
test -z "/usr/local/info" || mkdir -p -- . "/usr/local/info"
mkdir: cannot create directory `/usr/local/info': Permission denied
make[3]: *** [install-info-am] Error 1
make[3]: Leaving directory `/home/krishna/Software/gmp-4.2.4/doc'
make[2]: *** [install-am] Error 2
make[2]: Leaving directory `/home/krishna/Software/gmp-4.2.4/doc'
make[1]: *** [install-recursive] Error 1
make[1]: Leaving directory `/home/krishna/Software/gmp-4.2.4'
make: *** [install] Error 2
krishna@krishna-laptop:~/Software/gmp-4.2.4$ su
Password:
su: Authentication failure
krishna@krishna-laptop:~/Software/gmp-4.2.4$

          The problem remains remains unsolved when i enter su
and then correct password of root, the same error occurs as above.

          Please help.

            Thank you.

[Данило Шеган (danilo)]

This is not Launchpad bug, but a question about how to use Ubuntu.