Recently I did a software update and ASDM on Cisco ASA 5505. I encountered the following problem. The device had over year uptime and when I tried to copy software from TFTP server, I received a message – “read-only file system”. This caused me a little consternation.

ciscoasa# copy tftp flash

Address or name of remote host []? 10.1.1.83

Source filename []? asa921-k8.bin

Destination filename [asa921-k8.bin]?

Accessing tftp://10.1.1.83/asa921-k8.bin...!!!!!!!!!!!!!!!!!!!!!!!

...

Writing file disk0:/asa921-k8.bin...

%Error opening disk0:/asa921-k8.bin (Read-only file system)
ciscoasa#

Similar cases I have seen on Linux servers that were not properly turned off, but what the hell is this ??? Well, the fact that the Software ASA is also based on Linux. What’s more, the Linux fsck command to repair the file system is also present on the Cisco ASA.

And now fix the problem

ciscoasa# fsck disk0
dosfsck 2.11, 12 Mar 2005, FAT32, LFN
Reclaimed 27 unused clusters (106496 bytes) in 3 chains.
Performing changes.
/dev/hda1: 48 files, 10061/31033 clusters

fsck of disk0: complete
ciscoasa#

Now, it was possible to copy all necessary files.