How do I identify the distro on a cd, DVD or USB drive without booting it?
 

I have a number of USB Memory Sticks and some CD/DVDs with either Live or Installed Distros on. If I plug them in which File/Folder do I look at to identify the Distro and Version etc without having to boot them.

/etc - most of the time it should be pretty obvious which file(s) to cat. But varies by distro.

Searching /etc would be true for an installed distribution but not necessarily for a live version. There could be a readme file that contains the distribution/version. For some it isn't obvious by just mounting the drive/CD and looking at the contents.

cat /etc/*issue /etc/*release

but with many .isos it does not help, because there's no /etc directory.

you really have to look at the / files & directories; usually there's some sort of README.

Often the filesystem label in the ISO will tell you. You can use the file command to see it.(I deliberately gave the file a non-descriptive name just to demonstrate.)

For a physical disk in a drive, use "file -s /dev/cdrom" (or whatever device name is appropriate).

Most live distributions use a squashfs image for their filesystem, so if the advice given above doesn't work just install squashfs-tools and mount the image, the look for /etc/os-release (virtually any distribution nowadays has tat file).

Same problem. That's what we get for keeping lots of installation DVDs without properly labeling them.

What I did was to mount the ISO files temporarily, then handpicked files which appear to be informational text files.

Sample from the Centos7 minimal iso: