Bug #6440
open
VTY: 'write file' breaks 'show startup-config'
Added by fixeria 27 days ago.
Updated 23 days ago.
Description
In my understanding, show startup-config is supposed to show the initial config file that was loaded during the process startup. However, saving the current configuration by doing write file [FILE] currently breaks show startup-config:
$ ./tests/vty/vty_transcript_test -c ./tests/vty/vty_transcript_test.cfg
<0000> telnet_interface.c:88 Available via telnet 127.0.0.1 42042
$ telnet localhost 42042
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Welcome to the vty_transcript_test VTY interface
vty_transcript_test> en
vty_transcript_test# show startup-config
line vty
no login
vty_transcript_test# write file /tmp/backup.cfg
Configuration saved to /tmp/backup.cfg
vty_transcript_test# show startup-config
!
! vty_transcript_test (1.9.0.195-f2ea) configuration saved from vty
!!
!
line vty
no login
!
It gets even worse if saving the configuration fails for whatever reason:
vty_transcript_test# write file /dev/null
Can't open configuration file /dev/null.ul7SbU.
vty_transcript_test# show startup-config
vty_transcript_test#
- Status changed from New to Feedback
Here is a simple patch fixing the problem for me:
https://gerrit.osmocom.org/c/libosmocore/+/36617 vty: fix 'write file FILE' breaking 'show startup-config' [NEW]
However, we still have more things to consider:
show startup-config simply read()s the file (path stored in host.config), doing fopen()/fclose()
- so this actually reflects the current state of the config file, not the startup state
- any changes made to the config file after the startup will be shown
- this command will fail if the config file gets removed
- we could probably keep the file open (linux would keep a "frozen" copy for us)?
- in osmo-bsc.git, we have CTRL commands for loading config snippets
- AFAICS, those commands also change
host.config and thus break show startup-config
I didn't even know that 'show startup-config' existed. It would be fine with me to simply remove it.
fixeria wrote in #note-1:
- we could probably keep the file open (linux would keep a "frozen" copy for us)?
doesn't work if the file gets modified meanwhile. The safest choice is to keep a copy of the file in memory. Given the size of those files it's unlikely an issue.
I didn't even know that 'show startup-config' existed. It would be fine with me to simply remove it.
same for me.
I often use 'show running-config', i.e. showing the VTY as modified by the
current VTY session. Even that is ambiguous, it is not necessarily showing the
config that is in actual running use, for items that require a service restart.
(How does 'show startup-config' even work, do we cache the full cfg file contents?)
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