as root strace of: mkdir -p /usr/local/man/man1:
mkdir("/usr", 0755)                     = -1 EEXIST (File exists)
chdir("/usr")                           = 0
mkdir("local", 0755)                    = -1 EEXIST (File exists)
chdir("local")                          = 0
mkdir("man", 0755)                      = 0
open("man", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW) = 3
fchdir(3)                               = 0
close(3)                                = 0
mkdir("man1", 0755)                     = 0