there are lot of inbuilt tools that would suffice for a casual non antidebugged
application

first and formost
objdump for switches
try man -k objdump
or objdump --help

next is gdb the debugger that comes along with almost all standard
installation

man -k gdb or try gdb --help for help

probably some tracing tools like strace ptrace etc come bundled along
too

then there are external programs like hte the hexeditor that shows xrefs etc too
fenris,kdb,linice last but not least ida pro freeware also has a elf loader
there is linux version of idapro too

there are some very good reversing articles floating around on net
especially dealing with linux reversing

btw as JMI would say google is your best friend