Manage a server via the serial port (permission problems)

cu -l ttyS0 -s 115200
cu: open (/dev/ttyS0): Permission denied
cu: ttyS0: Line in use

ls -l /dev/ttyS0
crw------- 1 root root 4, 64 feb 19 08:54 /dev/ttyS0

find /sys -name dev | grep ttyS0
/sys/class/tty/ttyS0/dev
/etc/udev/rules.d# udevinfo -a -p /sys/class/tty/ttyS0
 
Udevinfo starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.
 
  looking at device '/class/tty/ttyS0':
    KERNEL=="ttyS0"
    SUBSYSTEM=="tty"
    DRIVER==""
 
  looking at parent device '/devices/pnp0/00:08':
    KERNELS=="00:08"
    SUBSYSTEMS=="pnp"
    DRIVERS=="serial"
    ATTRS{id}=="PNP0501"
 
  looking at parent device '/devices/pnp0':
    KERNELS=="pnp0"
    SUBSYSTEMS==""
    DRIVERS==""

echo SUBSYSTEM=="tty", KERNEL=="ttyS0", OWNER="uucp" > /etc/udev/rules.d/00-my.rules

gpasswd -a <youruser> dialout

ls -l /dev/ttyS0
crw-rw---- 1 uucp dialout 4, 64 feb 30 00:29 /dev/ttyS0
 
cu -l ttyS0 -s 115200
Connected.