For faster initial connection times, TRAMP stores previous
connection properties in a file specified by the user option
tramp-persistency-file-name.
The default file name for tramp-persistency-file-name is
~/.emacs.d/tramp.
TRAMP reads this file during Emacs startup, and writes to it when exiting Emacs. Delete this file for TRAMP to recreate a new one on next Emacs startup.
Set tramp-persistency-file-name to nil to disable
storing connections persistently.
When TRAMP detects a change in the operating system version in
a remote host (via the command uname -sr), it flushes all
connection related information for that host and creates a new entry.