Why Does Wq In Vim Fail With E45 Or A Read-Only File?

If you're short on time, here's the quick intuition: E45 means Vim won't let you write because the buffer is marked readonly. That isn't always a filesystem permission problem — sometimes it's purely a Vim flag — but they look similar until you inspect them.

First look inside Vim: run :set readonly? and :set modifiable? to see the buffer state. If readonly is on, try :w! or :wq! to force the write; you can also flip it with :set noreadonly. If the force still fails, check the OS level: run ls -l on the file or stat it to see ownership and mode. If you lack write permission, chmod or chown (if you can), or save with elevated rights using :w !sudo tee % >/dev/null or reopen with sudoedit. Another scenario is the filesystem is mounted read-only (like a stuck USB or an emergency remount) — check mount or dmesg.

I like keeping a tiny checklist in my head: buffer readonly? -> :set/noreadonly or :w!; permission denied? -> chmod/chown or sudo write; immutable attribute? -> chattr -i. It sounds like a lot, but once you've fixed it a couple of times it becomes muscle memory.

Oh, this one used to trip me up too, and once you see the little differences it's way less scary. E45 in Vim literally means the 'readonly' option is set for the buffer — Vim is telling you it won't overwrite what's flagged readonly unless you explicitly force it. That readonly flag can come from a few places: you opened the file with 'view' or 'vim -R', a modeline or your personal config set the buffer to readonly, or Vim detected that the file itself is write-protected by the OS (so even if you force it, the system will still stop you).

In practice that means two different things to check. First, inside Vim check the buffer option: :set readonly? or :echo &readonly will show whether the buffer is flagged. If that's the culprit you can clear it with :set noreadonly or just force the write with :w! or :wq!. Second, if forcing still fails you'll hit other messages like "E212: Can't open file for writing" or a plain permission denied — that's the operating system saying you don't have write access. Fix that by adjusting permissions (chmod u+w file), changing ownership (chown), remounting the filesystem read-write, or removing an immutable attribute (chattr -i file).

A practical trick I use when I forgot to start Vim with sudo: :w !sudo tee % >/dev/null will write the buffer as root, or just re-open the file with sudoedit. If you're unsure why Vim set readonly in the first place, :verbose set readonly? will often tell you which script or command changed it. Little habits like checking :set readonly? and ls -l outside Vim save me from frantic typing at 3 a.m.

When I first saw E45 I thought Vim was being dramatic, but it really boils down to two layers: Vim's own 'readonly' buffer flag and the OS-level write protection. Start by checking the buffer with :set readonly? and :set modifiable? — if the buffer is readonly you can either unset that option (:set noreadonly) or force the save with :w! or :wq!. If forcing still fails, check file permissions outside Vim with ls -l or stat; you might need chmod, chown, or to write as root. There's also the edge case of the filesystem being mounted read-only or the inode being immutable (chattr +i), which requires remounting or removing the attribute. For quick rescue writes I often do :w !sudo tee % >/dev/null to bypass permission issues without leaving Vim. Finally, :verbose set readonly? can point to the script or modeline that set Vim's readonly, which helps if this keeps happening and you want to fix the root cause.