agetty: handle systems without a shell or /bin/login#4437
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When the login program (default /bin/login, or the one set with
--login-program) is missing or not executable, logging in is impossible.
Previously agetty still displayed the issue file and prompted for a
username, producing a confusing dead end.
Before prompting, check whether the login program is executable with
access(X_OK). If it is not, print a short banner ("This system does not
permit logins." by default, configurable with --nologin-message) and
wait for the user to press Enter, then re-check so an administrator who
installs the login program at runtime can proceed without a reboot. The
normal prompt flow is unaffected when the login program exists.
Add --nologin-message to override the banner text and document the new
behavior in agetty.8.adoc.
Closes util-linux#4117
Contributor
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Lovely! thank you! |
keszybz
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Jun 22, 2026
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| /* Wait for Enter, then re-check the login program. */ | ||
| if (getc(stdin) == EOF) | ||
| return; | ||
| } |
Contributor
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Does this actually wait for Enter? It seems any key would work, if the input is not buffered. If it is buffered, it'd wait until Enter, and then do a tight loop. I think the EOF condition shouldn't fire, if this is connected to a console. I don't understand this loop.
Collaborator
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Thanks! Notes:
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Address review notes from Karel: reword DEFAULT_NOLOGIN_MESSAGE so it tells the user a keypress re-checks for the login program, and skip wait_for_login_program() when --chroot is used since the path check would test the wrong root. Update the man page accordingly. Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Contributor
Author
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Both notes addressed in 6a187af: the default message now reads 'Login is currently unavailable. Press any key to check again.' (which matches the actual behavior - the wait is a getc, so any key triggers the re-check), and wait_for_login_program() is skipped when --chroot is set, since the pre-chroot path check would test the wrong root. Man page updated to match. |
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Summary
Make agetty handle systems that have no shell and therefore no
/bin/login. Before showing the issue file and prompting for a username, agetty now checks whether the login program is executable. If it is not, agetty prints a short banner instead of prompting, and waits for the user to press Enter to re-check.A new
--nologin-messageoption lets the banner text be customized. The default message is "This system does not permit logins."Why this matters
This implements the request in #4117. Today agetty displays the issue file and prompts for a username even when login is impossible, producing a confusing dead end for the user. The behavior:
/bin/login, or the program set with--login-program) is missing or not executable, agetty prints the banner and does not prompt for a username or attempt to spawn login.access(X_OK)check, so an administrator who installs the login program at runtime can proceed without rebooting. If it is still missing, the banner is shown again.The check uses the resolved login path (
op->login, defaulting to_PATH_LOGIN), so pointing-l/--login-programat a non-existent path triggers the same behavior.Testing
util-linux builds on Linux only, so the change was validated by code review and a standalone syntax check of the new function (
gcc -Wall -Wextra -fsyntax-only, clean). The CI build will exercise the full compile.Manual scenarios to verify:
-lpointing at a non-existent path: same banner behavior.Closes #4117