My phone (galxy S2 plus) isn't detect when i connect it to my computer. I use ubuntu 18.04

Reboot and log in to the OS. Let the system settle and run:

echo "before"; echo; lsusb; echo

Connect the phone and wait a few seconds then run:

echo "after"; dmesg | tail; lsusb

What is the full output please?

Hi,
Thank you for you interest. Here is the output after having enter what you advise me above:

deepresistance@deepresistance-Latitude-E4310:~$ echo"before";echo;lsusb;echo
echobefore : commande introuvable

Bus 002 Device 003: ID 0a5c:5800 Broadcom Corp. BCM5880 Secure Applications Processor
Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0461:4db1 Primax Electronics, Ltd
Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

deepresistance@deepresistance-Latitude-E4310:~$ echo"after";dmesg | tail; lsusb
echoafter : commande introuvable
[ 6.693943] IPv6: ADDRCONF(NETDEV_UP): wlp2s0: link is not ready
[ 6.761552] IPv6: ADDRCONF(NETDEV_UP): wlp2s0: link is not ready
[ 10.103890] rfkill: input handler disabled
[ 13.202528] wlp2s0: authenticate with a0:21:b7:e5:53:2b
[ 13.236052] wlp2s0: send auth to a0:21:b7:e5:53:2b (try 1/3)
[ 13.239099] wlp2s0: authenticated
[ 13.244151] wlp2s0: associate with a0:21:b7:e5:53:2b (try 1/3)
[ 13.247538] wlp2s0: RX AssocResp from a0:21:b7:e5:53:2b (capab=0x411 status=0 aid=6)
[ 13.254302] wlp2s0: associated
[ 13.320917] IPv6: ADDRCONF(NETDEV_CHANGE): wlp2s0: link becomes ready
Bus 002 Device 003: ID 0a5c:5800 Broadcom Corp. BCM5880 Secure Applications Processor
Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0461:4db1 Primax Electronics, Ltd
Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Have a good day

Are you sure the cable is good? Does the phone show as charging when you connect it as well?

Have you tried a different cable and a different USB port?

I think you are right something goes wrong with the cable ! It does charge the phone so i didn't had any doubt about it. But i just try to connect it to an other computer with windows and it can't be detect neither.
By the way, i just have one usb port on my computer.
I will see if i can find an other cable to let you know.

Have a good day

At the end after having try my phone on others computer, it seems that the problem don't come from the cable but maybe directly the phone. At least it doesn't comes from Ubuntu. So, i will see how to fix that. Thanks again for your help.
Have a good day