The same bug is still present in `ssh-add` as of openssh-client
`1:10.0p1-5ubuntu5.4` on Ubuntu 25.10.
The fix in `1:7.4p1-5` covered the `ssh` client but not `ssh-add`'s passphrase
prompting code path.
**Observed behaviour:** Two `ssh-add` processes each consumed ~40% CPU
continuously for over 3 days (accumulating ~1727 CPU minutes each)
without printing any output or exiting. Both were loading the same
passphrase-protected key:
/usr/bin/ssh-add /home/martin/.ssh/AICID.private
Process state was `Rs` (running, session leader) — confirmed busy-
spinning, not blocked on I/O.
**Root cause (same as original bug):** The key has a passphrase
(confirmed via `ssh-keygen -y -P "" -f ~/.ssh/AICID.private` →
"incorrect passphrase"). When `ssh-add` was launched without a
controlling TTY, it attempted to prompt for the passphrase via
`tcsetattr()`, received `SIGTTOU`, and the syscall restarted in a tight
loop indefinitely rather than failing with an error.
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https://bugs.launchpad.net/bugs/1646813
Title:
ssh (client) stucks in an endless loop with 100% CPU
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