I ran into this recently where a Cisco ASA was powered off accidentally, and lost a whole month of config changes. The firewall still operated because it still had a config, just nothing from a month ago.
I then decided to log into the Cisco ASA and type “write mem” and got the following error.
Result of the command: "write mem"
Building configuration...
Cryptochecksum: 22387bc0 13130870 b142ffd2 c97d2014
%Error opening disk0:/.private/startup-config (Read-only file system)
Error executing command
[FAILED]
This is what Cisco had to say about the issue.
Error when wr mem command issued
This error appears when you try to save the configuration with the wr mem command:
%Error opening disk0:/.private/startup-config (Read-only file system)
Error executing command
In order to resolve this, perform a filesystem check so that the error can be removed. This command sequence is presented for your reference.
CiscoASA# wr mem
Building configuration…
Cryptochecksum: 2e24ca48 2496fe80 51a4ecbb 81a2dba5%Error opening disk0:/.private/startup-config (Read-only file system)
Error executing command
[FAILED] CiscoASA# fsck disk0fsck of disk0: complete
CiscoASA#
pehac-a0-df01# fsck flashfsck of flash: complete
CiscoASA# wr mem
Building configuration…
Cryptochecksum: 2e24ca48 2496fe80 51a4ecbb 81a2dba522851 bytes copied in 3.400 secs (7617 bytes/sec)
[OK]
What really grinds my gears is that I didn’t get a notification from ASDM GUI that the “write mem” command failed!
Here’s more information from Ciscos website:
http://www.cisco.com/en/US/products/ps6120/products_tech_note09186a0080b95d3d.shtml