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This is some additional clarification for what @Rasoul wrote.

'myuser' is in the 'dialout' group.

That is normally all that is required, but robot_upstart works a bit different. From the robot_upstart 0.2.0 documentation » The install script - permissions:

It’s important to understand how permissions work robot_upstart:

1. The upstart job invokes its jobname-start bash script as root.

2. The script sets up environment variables, and then uses setuidgid to execute roslaunch as an unprivileged user. This is by default the user who ran the install script, but it can also be specified explicitly via a flag.

3. The roslaunch which executes does not have its user’s group memberships. This means that it will not have access to serial ports with the dialout group, or locations in /var/log owned by root, etc. Any filesystem resources needed by your ROS nodes should be chowned to the same unprivileged user which will run ROS, or should set to world readable/writeable, for example using udev.

So jobname-start starts out as user root, but then quickly drops all privileges and continues as a regular user (that is not a member of the dialout group). That is why some more configuration is required.

This is some additional clarification for what @Rasoul wrote.

'myuser' is in the 'dialout' group.

That is normally all that is required, but robot_upstart works a bit different. From the robot_upstart 0.2.0 documentation » The install script - permissions:

It’s important to understand how permissions work robot_upstart:

1. The upstart job invokes its jobname-start bash script as root.

2. The script sets up environment variables, and then uses setuidgid to execute roslaunch as an unprivileged user. This is by default the user who ran the install script, but it can also be specified explicitly via a flag.

3. The roslaunch which executes does not have its user’s group memberships. This means that it will not have access to serial ports with the dialout group, or locations in /var/log owned by root, etc. Any filesystem resources needed by your ROS nodes should be chowned to the same unprivileged user which will run ROS, or should set to world readable/writeable, for example using udev.

So jobname-start starts out as user root, but then quickly drops all privileges and continues as a regular user (that is not a member of the dialout group). That is why some more configuration is required.