Using chkfsys on a live system

The chkfsys utility normally requires exclusive use of the filesystem to provide a comprehensive verification of the disk.

There is some risk in running chkfsys on a live system—both chkfsys and the filesystem are reading and possibly writing the same blocks on the disk.

If you do this, and chkfsys writes something, it sends a message to the filesystem to invalidate itself, and that makes the filesystem remount itself and go back to the disk to reread all data. This marks any open files as stale; you'll get an error of EIO whenever you read or write, unless you close and reopen the files. This can affect things such as your system log file.

Static changes, in place, on files or directories that the filesystem doesn't currently have opened will probably not cause problems.

If you're running an application that can't afford downtime or you couldn't run chkfsys because files were open for updating, try to run chkfsys with the -f option:

chkfsys -f /dev/hd0t79

This invokes a special read-only mode of chkfsys that can give you an idea of the overall sanity of your filesystem.