panel 1:

Every process on Linux has a PID (process ID) like 42.

In /proc/42, there’s a lot of VERY USEFUL information about process 42.

panel 2: /proc/PID/cmdline

command line arguments the process was started with.

panel 3: /proc/PID/environ

all of the process’s environment variables

panel 4: /proc/PID lexe

Symlink to the process’s binary magic: works even if the binary has been deleted!

panel 5: /proc/PID/status

Is the program running or asleep? How much memory is it using? And much more!

panel 6: /proc/PID/fd

Directory with every file the process has open!

Run $1s-1 /proc/42/fd to see the list of files for process 42.

These symlinks are also magic & you can use them to recover deleted files

panel 7: /proc/PID/stack

The kernel’s current stack for the process. Useful if it’s stuck in a system call.

panel 8: /proc/PID/maps

List of process’s memory maps. Shared libraries, heap, anonymous maps, etc.

panel 9: and more

Look at man proc for more information!