How do I know if I have installed the 64 bit version of R on Ubuntu?

"Use the 'file' command to determine the format of an executable (or any other file with a standard header). For example:

2 ~$ file /bin/bash
/bin/bash: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, stripped
3 ~$ file /lib/libpcre.so.3.12.1
/lib/libpcre.so.3.12.1: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, stripped
4 ~$

In this case, both the file and the library are 64-bit."