Not reading ~/.vimrc
Once you've loaded vim, :scriptnames
will tell you exactly what Vim read.
For me, it starts like this:
1: /Applications/MacVim.app/Contents/Resources/vim/vimrc
2: ~/.vimrc
3: /Applications/MacVim.app/Contents/Resources/vim/runtime/syntax/syntax.vim
4: /Applications/MacVim.app/Contents/Resources/vim/runtime/syntax/synload.vim
5: /Applications/MacVim.app/Contents/Resources/vim/runtime/syntax/syncolor.vim
IF you want to check where a particular setting is being set, use "verbose set". For example, :verbose set background
tells me:
background=light
Last set from ~/.vimrc
so I know that my setting in ~/.vimrc is being read, and that none of the later files is clobbering it.
if you're on linux and want to know if vim is accessing your ~/.vimrc on startup you can launch it with strace:
strace -o vim_strace vim
then quit vim. Open the vim_strace file and search for "vimrc" in the file. you should find a line like that
stat64("/home/youruser/.vimrc", {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
which mean that at least vim sees the file.