There unfortunately isn't a command to hardlink the file. ln will fail, because /proc is a different filesystem: anthony@Zia:/proc/28590/fd$ ln 4 /tmp/bar

There unfortunately isn't a command to hardlink the file. ln will fail, because /proc is a different filesystem: anthony@Zia:/proc/28590/fd$ ln 4 /tmp/bar ln: creating hard link `/tmp/bar' => `4': Invalid cross-device link Linux's link(2) call takes path names, not file descriptors, so even a ptrace inject into the still-running app won't help. I don't believe its (currently) possible to re-link the file, without direct filesystem editing.