12.1 Identifying files
When a source file has been compiled to an object file or executable the
options used to compile it are no longer obvious. The
command looks at the contents of an object file or executable and
determines some of its characteristics, such as whether it was compiled
with dynamic or static linking.
For example, here is the result of the
file command for a typical
$ file a.out
a.out: ELF 32-bit LSB executable, Intel 80386,
version 1 (SYSV), dynamically linked (uses shared
libs), not stripped
The output shows that the executable file is dynamically linked, and
compiled for the Intel 386 and compatible processors. A full
explanation of the output is shown below:
The internal format of the executable file (ELF stands for "Executable
and Linking Format", other formats such as COFF "Common Object File
Format" are used on some older operating systems (e.g. MS-DOS)).
The word size (for some platforms this would be 64-bit).
Compiled for a platform with least significant byte first
word-ordering, such as Intel and AMD x86 processors (the alternative MSB
most significant byte first is used by other processors, such as
the Motorola 680x0)(36). Some
processors such as Itanium and MIPS support both LSB and MSB orderings.
The processor the executable file was compiled for.
version 1 (SYSV)
This is the version of the internal format of the file.
The executable uses shared libraries (
statically linked indicates
programs linked statically, for example using the
The executable contains a symbol table (this can be removed with the
file command can also be used on object files, where it
gives similar output. The POSIX standard(37) for Unix systems defines the behavior