In my Nexus 5 device, I can see the kernel version as follows:
I know 3.4.0 is the linux kernel version number, and d59db4e is short of a commit sha1. here is another example.
I just wonder: What does it mean by letter 'g'?
It stands for git, the name of the version control system used for the Linux kernel. Git itself isn't an abbreviation, it's just the name of the system. The
git describe command is what's used to generate these version identifiers, and its manpage describes the format:
The hash suffix is "-g" + 7-char abbreviation for the tip commit of parent ... The "g" prefix stands for "git" and is used to allow describing the version of a software depending on the SCM the software is managed with. This is useful in an environment where people may use different SCMs.