how to see the verbose output of a process that is running that writes to a file (shred)

I am running the shred command to securely wipe some storage.

I would like to see its progress, but have lost the ssh terminal that was running the command.

Is there a way that I can use to see the verbose output of the shred command from a new ssh terminal?

I have tried to hook into and view the output from /proc/pid/fd/0 1 2 etc but it just shows the random characters from /dev/urandom. I tried using strace, but the same file descriptors were available, with the same results. Shred shows 0, 1, 2, 3, and 4 fd, but they are all showing the random output.

MTIA, waiting patiently with stethoscope against drive...

On Linux (since OP mentioned /proc/pid/fd/0 which is a Linux thing), for any tool that is doing sequential operations, the method below in 3 steps can be used:

1. Figure out the PID of the tool

   eg:

   # pgrep ^shred$
   699
   

2. Note for this PID the file descriptor(s) of interest that is reading or writing

   For example with ls -l /proc/<pid>/fd/ or stat -c %N /proc/<pid>/fd/<FD> or lsof ... ...

   Example:

   # ls -l /proc/699/fd/
   total 0
   lrwx------ 1 root root 64 May 24 11:40 0 -> /dev/pts/6
   lrwx------ 1 root root 64 May 24 11:40 1 -> /dev/pts/6
   lrwx------ 1 root root 64 May 24 11:40 2 -> /dev/pts/6
   l-wx------ 1 root root 64 May 24 11:40 3 -> /dev/loop7
   

   Here the FD of interest is 3. It could have been FD 4 (like appears to be OP's case in this comment) or any other, depending on the command, the version of this command or its options when invoked.

3. Query the kernel, using /proc/<pid>/fdinfo/<fd> about additional information:

   /proc/[pid]/fdinfo/ (since Linux 2.6.22)

   [...] The files in this directory are readable only by the owner of the process.

   (or by root or at least a process with the adequate capability.)

   The contents of each file can be read to obtain information about the corresponding file descriptor. [...]

   The fields are as follows:

   pos This is a decimal number showing the file offset.
   [...]

   For example:

   # cat /proc/699/fdinfo/3
   pos: 286785536
   flags:   0140001
   mnt_id:  830
   ino: 39
   

   or:

   # awk '/^pos:/ { print $2 }' /proc/699/fdinfo/3
   286785536
   

   So in this example shred is currently writing at position 286785536 ( ~ 273MiB).

This method doesn't require any cooperation from the tool: it doesn't have to be run in a terminal, be run in verbose mode, have any text output anywhere, log anything anywhere, to support handling a special signal (like dd does) to dump information, nor be ptrace()-ed: the kernel provides the current information through /proc.