Binaries are usually [stripped][1]. For ELF binaries, you can check it with `file` command

    $ file /bin/true
    /bin/true: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.26, BuildID[sha1]=0x73796652ea437df8ac7b3ba1864a7ac177e27600, stripped

Notice the `stripped` at the end of file's result. It means, among other things, that symbols have been removed, so it won't find `main` function. 

In order to run the binary and stop the debugger right after the load, there is some **kind of** universal method that should almost always work (kind of universal, not 100%)

You have to find the entry point, retreived by this command :

    $ readelf -h /bin/true | grep "Entry point"
      Entry point address:               0x401264

Then load the binary into your favourite debugger (lldb, gdb, ...) and break on this address.

**lldb :**

    (lldb) br s -a 0x401264
    Breakpoint 1: address = 0x0000000000401264
    (lldb) r
    ...
    (lldb)
    

**gdb :**

    $ gdb -q /bin/true
    Reading symbols from /bin/true...(no debugging symbols found)...done.
    gdb$ b *0x401264
    Breakpoint 1 at 0x401264
    gdb$ r
    Breakpoint 1, 0x0000000000401264 in ?? ()
    gdb$

Once you've loaded your binary and your breakpoint has been triggered, you can display following instructions this way :

**lldb :**

    (lldb) (lldb) x -s4 -fi -c11 $pc
    -> 0x401264:	xor    ebp,ebp
       0x401266:	mov    r9,rdx
       0x401269:	pop    rsi
       0x40126a:	mov    rdx,rsp
       0x40126d:	and    rsp,0xfffffffffffffff0
       0x401271:	push   rax
       0x401272:	push   rsp
       0x401273:	mov    r8,0x403560
       0x40127a:	mov    rcx,0x403570
       0x401281:	mov    rdi,0x4011c0
       0x401288:	call   0x401060 <__libc_start_main@plt>

**gdb :**

    gdb$ x/11i $pc
    => 0x401264:	xor    ebp,ebp
       0x401266:	mov    r9,rdx
       0x401269:	pop    rsi
       0x40126a:	mov    rdx,rsp
       0x40126d:	and    rsp,0xfffffffffffffff0
       0x401271:	push   rax
       0x401272:	push   rsp
       0x401273:	mov    r8,0x403560
       0x40127a:	mov    rcx,0x403570
       0x401281:	mov    rdi,0x4011c0
       0x401288:	call   0x401060 <__libc_start_main@plt>

`i` flag means **i**nstruction, and `$pc` means **P**rogram **C**ounter (equivalent of EIP/RIP for 32/64 bits architecures). You can see that [__libc_start_main][2] will be called at address `0x401288`. Its man page indicates its first argument is a pointer to binary `main` function. 1st argument is here loaded in `rdi` register, meaning that `main` function is located at address `0x4011c0`.

You just have to finally place a breakpoint at this address (`0x4011c0`) and you'll be at the beginning of your binary main function.
 
Good luck and have fun !


  [1]: https://en.wikipedia.org/wiki/Strip_%28Unix%29
  [2]: http://refspecs.linuxbase.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/baselib---libc-start-main-.html