[shell] Update kill completion

* Explicitly specify the list of fields for consistent experience
* Add fallback command for BusyBox (Close #3219)
* Apply `--header-lines=1` to show the column header

shell/completion.bash

@@ -270,8 +270,9 @@ _fzf_complete_kill() {
 }
 
 _fzf_proc_completion() {
-  _fzf_complete -m --preview 'echo {}' --preview-window down:3:wrap --min-height 15 -- "$@" < <(
-    command ps -ef | sed 1d
+  _fzf_complete -m --header-lines=1 --preview 'echo {}' --preview-window down:3:wrap --min-height 15 -- "$@" < <(
+    command ps -eo user,pid,ppid,start,time,command 2> /dev/null ||
+      command ps -eo user,pid,ppid,time,args # For BusyBox
   )
 }
 

shell/completion.zsh

@@ -251,8 +251,9 @@ _fzf_complete_unalias() {
 }
 
 _fzf_complete_kill() {
-  _fzf_complete -m --preview 'echo {}' --preview-window down:3:wrap --min-height 15 -- "$@" < <(
-    command ps -ef | sed 1d
+  _fzf_complete -m --header-lines=1 --preview 'echo {}' --preview-window down:3:wrap --min-height 15 -- "$@" < <(
+    command ps -eo user,pid,ppid,start,time,command 2> /dev/null ||
+      command ps -eo user,pid,ppid,time,args # For BusyBox
   )
 }