Xsel problem with "tmux"

[Mehrdad ♑]

Hi, I use ubuntu 22.04
When I open tmux on my terminal and I wanna to use xsel show me this error:

$ hostname | xsel --clipboard --input
xsel: Can't open display: (null)
: Inappropriate ioctl for device

but, when I open a terminal without tmux, xsel is working good

[M Kelly]

Check your DISPLAY env variable when in tmux ?