Linking verbs are not used to show actions. They act as a link between the subject and the complement, which describes the subject. The complement is mostly an adjective or an adjective phrase although it can be a noun phrase or an adverbial. The complement gives more information about the subject.

Verbs that are always linking verbs:

Dedicated Linking Verbs
be* become seem

* and any form of the verb be.

Linking verbs that are any forms of the verb 'to be' are also helping verbs:

All eight forms of 'to be' are also helping verbs
is was been
am were being
are be  

The linking verbs are boldfaced in the following examples.  

Examples:

  • Sitting on a garden bench and watching people jogging past is my new hobby.

    (Complement = noun phrase: my new hobby)

  • Those trees are where owls roost and hoot at night.

    (Complement = adverbial phrase: where owls roost and hoot at night.)

  • This morning our boss was grumpy.

    (Complement = adjective: grumpy)

  • The graves of their parents were marked by simple headstones.

    (Complement = adjective phrase: marked by simple headstones.)

Verbs that are linking verbs and can also be action verbs:

Linking Verbs that can also be Action Verbs
act

grow

sound*

appear

look*

stay

feel*

prove

taste*

get

remain

turn

go

smell*

 

* sensory

Some linking verbs in verb phrases: 

Linking Verbs in Verb Phrases
can be

had been

should be

could be

may be

will be

has been

might be