I recently responded to another user in a Slack channel regarding this topic and thought I’d post it here as well. The discussion revolved around when you need to use the -- command demarcation with the kubectl exec command.
As for the necessity or not of the — command, it depends on what you’re doing. If you’re not passing any arguments to the command, it’s not needed.
Let’s create a new pod based on busybox to test the theory: kubectl run bb --image=busybox --restart=Never --command -- sleep 3600
If we want to list the directories with ls, we can do it your way:
$ kubectl exec bb ls
bin
dev
etc
home
proc
root
sys
tmp
usr
var
Let’s say we want to know more about the contents so we try to do a long listing. This will generate an error.
$ kubectl exec bb ls -al
Error: unknown shorthand flag: 'a' in -al
However, if we include the --, the command and argument(s) are handled properly and we get the desired results.
$ kubectl exec bb -- ls -al
total 44
drwxr-xr-x 1 root root 4096 Dec 8 21:17 .
drwxr-xr-x 1 root root 4096 Dec 8 21:17 ..
-rwxr-xr-x 1 root root 0 Dec 8 21:17 .dockerenv
drwxr-xr-x 2 root root 12288 Dec 2 20:12 bin
drwxr-xr-x 5 root root 360 Dec 8 21:17 dev
drwxr-xr-x 1 root root 4096 Dec 8 21:17 etc
drwxr-xr-x 2 nobody nogroup 4096 Dec 2 20:12 home
dr-xr-xr-x 238 root root 0 Dec 8 21:17 proc
drwx------ 2 root root 4096 Dec 2 20:12 root
dr-xr-xr-x 13 root root 0 Dec 8 21:16 sys
drwxrwxrwt 2 root root 4096 Dec 2 20:12 tmp
drwxr-xr-x 3 root root 4096 Dec 2 20:12 usr
drwxr-xr-x 1 root root 4096 Dec 8 21:17 var
Hopefully this will clear up any confusion.