Question

If I do the following command on my executable called "version", compiled on Fedora Core 11, I get this output

file version

version: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped

What s the significance of the 2.6.18 number towards the end, and is it any use in distinguishing to customers which version of some software they should download ?

From what I ve looked at so far, this number is definitely not

The kernel version
The libc version
Anything to do with the lsb_release

I d like to get some easy identifier to allow customers to know which binary release they should download, which they should ideally be able to identify by typing a command (like uname -a, although that obviously isn t the one in this case).

Thanks

Answer 1

It s the kernel version of the machine the binary was compiled on. If you use precompiled binaries from your distribution, it s the kernel version of a machine of the distribution vendor, probably in its compile farm.

It s relevant e.g. when considering syscalls. Say your binary uses the syscall no. X and you use a kernel which does not support X yet or worse has assigned syscall no. X to a different syscall.

The vanilla Linux Kernel User API is stable. That means every syscall available in Linux version A is available in Linux version B if A <=B. But it may happen that some developer releases his/her own development version of Linux (something like linux-2.6.18-xy) and s/he implements a new syscall. If s/he now compiles a binary using that kernel version, the binary gets tagged with that version. So, you are later on able to know that it may or may not work.

Btw, /usr/include/asm/unistd_32.h contains syscall numbers, excerpt:

[...]
#define __NR_restart_syscall      0
#define __NR_exit         1
#define __NR_fork         2
#define __NR_read         3
#define __NR_write        4
#define __NR_open         5
[...]

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