In order to find out about the syscalls in linux you can use quite a few sources. There are a few websites summarising the details quite nicely, one of these is http://quaff.port5.com/syscall_list.html
Alternatively if you have the kernel source you can look in the following files,
Or for a more low tech solution when nothing else is available you can dissassemble the C library binary. You should be able to deduce the syscalls and their meanings from this.
objdump -S libc.a