Symfony 2: How do I check if a user is not logged in inside a template?

You can check if app.user is set.

 {% if app.user %}
    # user is logged in
 {% else %}
    # user is not logged in
 {% endif %}

Although the current answer answers the OP's question, I would like to add more details.

I understand the OP did not want to check roles, but I am including them so other SO users can copy and paste from this in the future. - everytime I google this, I end up here!

Symfony Doc Sources:

• http://symfony.com/doc/current/book/security.html
• http://symfony.com/doc/current/cookbook/security/remember_me.html

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Check if any user logged in (regardless of role)

As answered, you can use app.user to check if any user is logged in.

{% if app.user %}
    # user is logged in (any and all users, regardless of ROLE_*)
{% elseif not app.user %}
    # user is not logged in (note the `not` in the `elseif` statement)
{% endif %}

---

Checking authentication status

You can use the is_granted() method to check for ROLES, (The below are all roles assigned by symfony, You may also have you own roles (more below))

{% if is_granted('IS_AUTHENTICATED_FULLY') %}
    # This user entered their credentials THIS session
{% elseif is_granted('IS_AUTHENTICATED_REMEMBERED') %}
    # User logged in via a cookie (ie: Auth again before doing sensitive things)
{% elseif is_granted('IS_AUTHENTICATED_ANONYMOUSLY') %}
    # This is a `guest` or anonymous user
{% endif %}

from the docs:

IS_AUTHENTICATED_ANONYMOUSLY - automatically assigned to a user who is in a firewall protected part of the site but who has not actually logged in. This is only possible if anonymous access has been allowed.

IS_AUTHENTICATED_REMEMBERED - automatically assigned to a user who was authenticated via a remember me cookie.

IS_AUTHENTICATED_FULLY - automatically assigned to a user that has provided their login details during the current session.

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Checking Roles

You can also use is_granted() to check for roles.
Assuming we have 3 roles (ROLE_SUPER_ADMIN, ROLE_ADMIN, & ROLE_USER)

{% if is_granted('ROLE_SUPER_ADMIN') -%}
    # You're `ROLE_SUPER_ADMIN`
{% elseif is_granted('ROLE_ADMIN') -%}
    # You're `ROLE_ADMIN`
{% elseif is_granted('ROLE_USER') -%}
    # You're `ROLE_USER`
{% else %}
    # You're a `nobody` ;P
{%- endif %}

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Doing the above inside a controller

View the following answer: How to check if an user is logged in Symfony2 inside a controller?