Bug 691406

Summary: RFE: Clear screen including scroll-back buffer before log-in
Product: [Fedora] Fedora Reporter: Petr Pisar <ppisar>
Component: mingettyAssignee: Petr Pisar <ppisar>
Status: CLOSED RAWHIDE QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: rawhideCC: ppisar
Target Milestone: ---Keywords: Patch
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: mingetty-1.08-8.fc16 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 714687 (view as bug list) Environment:
Last Closed: 2011-06-10 12:51:22 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 684261    
Bug Blocks:    
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Description Flags
Implementation none

Description Petr Pisar 2011-03-28 13:13:54 UTC 
There was a discussion (bug #681600) how to disable access to text printed by previous user on the console to prevent sensitive data leak.

mingetty should instruct Linux virtual terminal to clear screen including scroll-back buffer. Once Linux will implement it (bug #684261), adapt mingetty to perform the safe clear.

Because current behavior is not to clear the screen and there can be demand not to do it always (e.g. to debug broken login shell or to investigate init scripts output on /dev/console), new mingetty positional argument will be added to switch on/off the screen cleaning.
Comment 1 Petr Pisar 2011-06-10 09:38:26 UTC 
F16 delivers kernel-3.0* that supports \E[3;J to clear screen including scroll-back buffer.

F16 uses systemd as init that by default reallocate VT before spawning mingetty, thus the scroll-back buffer is always empty.

To test this bug report, one can use following command:

# openvt -f -c 10 -s -w -- /bin/bash \
  -c 'dmesg; exec /sbin/mingetty --loginprog=/bin/false tty10'

This allocates TTY10, switches console there, pollutes buffer with kernel log, and then executes mingetty. Now it's possible to press Shift-PgUp to verify the buffer has gone.

I will add new positional argument to mingetty to enable safe console clearing. The clearing will be done by issuing the the new escape sequence followed by the older 2J variant to clean at least current visible area if mingetty run on system not supporting the new 3J sequence.
Comment 2 Petr Pisar 2011-06-10 11:31:31 UTC 
Se there is already --noclear option defaulting to clear. So adding the new sequence seems to be enough.
Comment 3 Petr Pisar 2011-06-10 12:26:42 UTC 
Created attachment 504091 [details]
Implementation

Tested with Linux 3.0-0.rc2.git0.1.fc16.x86_64 on VGA console.