[linux][uart] open uart error

question

• Exitcode 2 - cannot open device /dev/ttyUSB0

microcom -s 115200 -p /dev/ttyUSB0
Usage: microcom [options]
 [options] include:
    -p, --port=<devfile>                 use the specified serial port device (/dev/ttyS0);
    -s, --speed=<speed>                  use specified baudrate (115200)
    -t, --telnet=<host:port>             work in telnet (rfc2217) mode
    -c, --can=<interface:rx_id:tx_id>    work in CAN mode
                                         default: (can0:200:200)
    -f, --force                          ignore existing lock file
    -d, --debug                          output debugging info
    -l, --logfile=<logfile>              log output to <logfile>
    -o, --listenonly                     Do not modify local terminal, do not send input
                                         from stdin
    -a,  --answerback=<str>              specify the answerback string sent as response to
                                         an ENQ (ASCII 0x05) Character
    -v, --version                        print version string
    -h, --help                           This help
Exitcode 2 - cannot open device /dev/ttyUSB0

Answer:
sudo permision

• Exitcode 3 - lockfile for port exists /dev/ttyUSB0

sudo microcom -s 115200 -p /dev/ttyUSB0

$ sudo microcom -s 115200 -p /dev/ttyUSB0
Usage: microcom [options]
 [options] include:
    -p, --port=<devfile>                 use the specified serial port device (/dev/ttyS0);
    -s, --speed=<speed>                  use specified baudrate (115200)
    -t, --telnet=<host:port>             work in telnet (rfc2217) mode
    -c, --can=<interface:rx_id:tx_id>    work in CAN mode
                                         default: (can0:200:200)
    -f, --force                          ignore existing lock file
    -d, --debug                          output debugging info
    -l, --logfile=<logfile>              log output to <logfile>
    -o, --listenonly                     Do not modify local terminal, do not send input
                                         from stdin
    -a,  --answerback=<str>              specify the answerback string sent as response to
                                         an ENQ (ASCII 0x05) Character
    -v, --version                        print version string
    -h, --help                           This help
Exitcode 3 - lockfile for port exists /dev/ttyUSB0

rm the lock file, for example: rm /var/lock/lockdev/LCK..ttyUSB0 / rm /var/lock/lockdev/*