I'm fairly new to Ubuntu and development on Linux in general. After building GDB from source (pre-installed the dependencies):
$ git clone git://sourceware.org/git/binutils-gdb.git
$ CD binutils-gdb
$ ./Configure
$ Make
$ Make Install
I tried:
$ gdb
and got the following:
bash: /usr/bin/gdb: No such file or directory
Opened up a new terminal, tried running GDB again, and got the expected output of:
GNU gdb (GDB) 8.1.50.20180123-git...
Wondering why it only worked after opening a new terminal.