How can I create a multiboot USB stick from Linux?

You can refer to https://www.pendrivelinux.com/multiboot-create-a-multiboot-usb-from-linux/

It works for me!

Above you can see that I am able to boot Ubuntu 16.03 as well as 18.04 with one USB stick w/o problem.

But somehow you've to disable security boot in BIOS.

Enjoy~

How can I setup a proxy server in Ubuntu 16.04?

Step1. Install package squid

# sudo apt-get install -y squid

Step2. To setup common proxy settings:

# sudo vi /etc/squid/squid.conf

To add some lines below:

# line 977

acl lan src 192.168.1.0/24

(where 192.168.1.0 means network you would like to allow client to access your proxy server)

# line 1189

http_access allow lan

(Allow lan here)

# line 1602

http_port 3128

(To modify default proxy port if needed)

Step3. Restart squid

# sudo systemctl restart squid

Step4. Examine squid service

# sudo systemctl status squid

● squid.service - LSB: Squid HTTP Proxy version 3.x

Loaded: loaded (/etc/init.d/squid; bad; vendor preset: enabled)

Active: active (running) since 四 2018-04-26 15:24:04 CST; 1min 56s ago

Docs: man:systemd-sysv-generator(8)

Process: 3088 ExecStop=/etc/init.d/squid stop (code=exited, status=0/SUCCESS)

Process: 3119 ExecStart=/etc/init.d/squid start (code=exited, status=0/SUCCESS)

CGroup: /system.slice/squid.service

├─3159 /usr/sbin/squid -YC -f /etc/squid/squid.conf

├─3161 (squid-1) -YC -f /etc/squid/squid.conf

├─3162 (logfile-daemon) /var/log/squid/access.log

└─3163 (pinger)

四 26 15:24:04 uc16-VirtualBox systemd[1]: Starting LSB: Squid HTTP Proxy version 3.x...

四 26 15:24:04 uc16-VirtualBox squid[3119]: * Starting Squid HTTP Proxy squid

四 26 15:24:04 uc16-VirtualBox squid[3159]: Squid Parent: will start 1 kids

四 26 15:24:04 uc16-VirtualBox squid[3119]: ...done.

四 26 15:24:04 uc16-VirtualBox systemd[1]: Started LSB: Squid HTTP Proxy version 3.x.

四 26 15:24:04 uc16-VirtualBox squid[3159]: Squid Parent: (squid-1) process 3161 started

# netstat -tupln | grep 3128

tcp6 0 0 :::3128 :::* LISTEN 3161/(squid-1)

Done ~

In proxy client side:

You can use tcpdump or wireshark to ensure that http request will go to proxy server after you configured http proxy server within browser.

root@server1:~$ sudo tcpdump -n -v -i any port 3128

tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes

15:29:06.382845 IP (tos 0x0, ttl 64, id 2257, offset 0, flags [DF], proto TCP (6), length 145)

192.168.1.211.40994 > 192.168.1.254.3128: Flags [P.], cksum 0x85a5 (incorrect -> 0x9ba8), seq 670754847:670754940, ack 314235908, win 237, options [nop,nop,TS val 1731217504 ecr 1884649606], length 93

15:29:06.383195 IP (tos 0x0, ttl 64, id 35299, offset 0, flags [DF], proto TCP (6), length 212)

192.168.1.254.3128 > 192.168.1.211.40998: Flags [P.], cksum 0xbf6c (correct), seq 2355697405:2355697565, ack 1986317666, win 486, options [nop,nop,TS val 1884649610 ecr 1731217476], length 160

15:29:06.383264 IP (tos 0x0, ttl 64, id 17423, offset 0, flags [DF], proto TCP (6), length 52)

192.168.1.254.3128 > 192.168.1.211.40994: Flags [.], cksum 0xaba6 (correct), ack 93, win 503, options [nop,nop,TS val 1884649610 ecr 1731217501], length 0

15:29:06.383359 IP (tos 0x0, ttl 64, id 2258, offset 0, flags [DF], proto TCP (6), length 1353)

192.168.1.211.40994 > 192.168.1.254.3128: Flags [P.], cksum 0x8a5d (incorrect -> 0x8fe0), seq 93:1394, ack 1, win 237, options [nop,nop,TS val 1731217505 ecr 1884649610], length 1301

15:29:06.384198 IP (tos 0x0, ttl 64, id 9911, offset 0, flags [DF], proto TCP (6), length 268)