If you’re trying to run rkhunter check on your server and finding expr: syntax error for all binaries, it might be due to outdated file properties database.
Run the following command to fix it:
rkhunter –propupd –update
After updating the file properties database, you must get rkhunter working fine again.
Here is some more information about –propupd option
–propupd [file | directory | Update the entire file properties database,
package]… or just for the specified entries