Zsh’s command completion for some commands is unacceptably slow. After a bit of digging, I discovered using an atypically large hosts file causes problems. A one-line customisation to Zsh solved the issue.
Tab completion on certain commands causes Zsh to use ~100% CPU time, rendering the system unresponsive.
Add the following to your
# Disable hostname completion zstyle ':completion:*' hosts off
Whenever I’d use tab completion on commands such as
ssh, my system would completely freeze. Zsh’s advanced command completion is
one of it’s killer features, so rather than switching back to Bash, this had
to be fixed.
A few unsuccessful DuckDuckGo1 searches later, I headed to the Zsh IRC
channel. One helpful user (thanks daethorian!) mentioned similar experiences
and alluded to the
As mentioned in a previous post, I use a custom hosts file as a lightweight alternative to browser ad-blocking. Unfortunately, this file is necessarily huge (~12,000 lines!), so it made sense for Zsh to die a slow death when trying to match a hostname.
The idea was to disable hostname completion. With a bit of perseverance with the zshcompsys(1) manual, I came up with:
zstyle ':completion:*' hosts off
:completion:* matches any context where tab completion can be used (any
command, path, glob etc).
hosts — the “tag” (or type of completion) —
accepts one parameter; either a path to a hosts file (defaulting to
/etc/hosts) or a boolean.