ranlib command in Linux with Examples

ranlib command in Linux is used to generate index to archive. ranlib generates an index to the contents of an archive and it will be stored in the archive. The index lists each symbol defined by a member of an archive which is simply a relocatable object file. You may use 'nm -s' or 'nm –print-armap' to list all of this index.

An archive with such an index speeds up the linking to the library and allows routines in the library to call each other without regard to their placement in the archive. The GNU ranlib program is another form of GNU ar; running ranlib is completely equivalent to running 'ar -s'.

Syntax

ranlib [--plugin name] [-DhHvVt] archive

Basic Example

It will generate an index to archive as shown in the below example.

Explanation: As you can see in above example we are archiving three files named main.o, point.o and rectangle.o to fruits.a and then using ranlib command generating an index to the contents of an archive and it will be stored in the archive.

Common Options Used with the ranlib command

Here are the key options you can use with ranlib:

1. --help:

This option displays usage information for the ranlib command, making it useful for users who need a quick reference on how to use the tool.

Example:

ranlib --help

2. --version:

This option shows the version of the ranlib command installed on your system.

Example:

ranlib --version

3. -D (Deterministic Mode):

This option will operate in deterministic mode. The symbol map archive of member's header will show zero for the UID, GID, and timestamp. When this option is being used, multiple runs will produce identical output files.

Example:

ranlib -D fruits.a

Explanation:

As you can see in above example we are archiving three files named main.o, point.o and rectangle.o to fruits.a and then using ranlib command with the option -D we are changing the mode of operation to deterministic and generating an index to the contents of an archive and it will stores it in the archive.

4. -t (Timestamp Update):

This option updates the timestamp of the symbol map within the archive. It is often used when updating existing archives to ensure the symbol map remains current.

Example :

ranlib -t fruits.a

5. -U (Non-Deterministic Mode):

This option do not operate in deterministic mode. This is exactly the inverse of the -D option. The archive index will get actual UID, GID, timestamp, and file mode values. If binutils was configured without using --enable-deterministic-archives, then this mode is set by default.

Example:

ranlib -U fruits.a

Conclusion

The ranlib command plays a vital role in the management of static libraries in Linux, particularly for C and C++ developers. By generating an index for an archive, ranlib enhances the efficiency of the linking process, enabling faster access to symbols and ensuring routines within the library can interact effectively. With options for deterministic and non-deterministic modes, ranlib also helps developers maintain reproducible builds, which is crucial in modern software development.