如何解決Lenovo X1 Carbon 6th 在Linux下無法休眠(S3)的問題？

是的這個問題困擾了我一陣子，今天上網搜尋了一下總算是找到了解決的方法。

首先確定把BIOS升級到1.30以上。(可以透過dmidecode查看)

接下來，將系統重新開機後進入BIOS去選擇: (Default設定是Win10)
Config -> Power -> Sleep State -> Set to Linux

到這邊已經完成了，系統測試一切正常！

Operating System: Ubuntu 18.04.2 LTS
Kernel: Linux 4.15.0-46-generic
Architecture: x86-64

Ubuntu 16.04.6 LTS 釋出囉！

Canonical最近釋出了Ubuntu 16.04.6 LTS更新版本，這一次的更新主要是針對修正APT相關的安全性問題(CVE-2019-3462)。

ISO檔案可以透過以下連結來下載:

http://releases.ubuntu.com/xenial/

另外APT的漏洞在14.04, 18.04, 18.10也都存在相同的問題，不過不用太擔心！只要透過一般的軟體更新機制就可以修正APT安全性的問題。

如何在Ubuntu 18.04.2建立一個anonymous FTP server?

FTP算是一個非常古老的檔案傳輸通訊協定，雖然現今已經不像以前那樣舉足輕重了，但是偶爾拿來使用一下還是挺方便的。

稍微紀錄一下如何在Ubuntu 18.04.2 Desktop建立一台anonymous FTP server。

安裝:

$ sudo apt update && apt install vsftpd

Ubuntu現在很好玩，當你安裝好任何一個service的時候，systemd就會自動把它enable與active，你可以透過以下的命令快速驗證一下:

$ systemctl status vsftpd
$ netstat -tupln | grep ftp

修改vsftpd.conf:
預設vsftpd並不允許anonymous去做檔案的上傳或下載，所以我們需要改變幾個參數讓它支援。

$ sudo vi /etc/vsftpd.conf
# Allow anonymous FTP? (Disabled by default).
anonymous_enable=YES

# Uncomment this to enable any form of FTP write command.
write_enable=YES

# Uncomment this to allow the anonymous FTP user to upload files. This only
# has an effect if the above global write enable is activated. Also, you will
# obviously need to create a directory writable by the FTP user.
anon_upload_enable=YES

改完之後記得重啟

$ sudo systemctl restart vsftpd

建立anonymous FTP folder:

Ubuntu預設的FTP server folder是在/srv/ftp，所以欲分享的檔案可以放在這邊。下圖你可以看到我share的檔案(左)可以被遠端的FTP client抓取(右)。

接下來建立一個folder pub under /srv/ftp來讓遠端user可以透過FTP上傳檔案。

$ cd /srv/ftp
$ sudo mkdir pub
$ sudo chmod 777 pub
$ sudo chown ftp.ftp pub

以上一個anonymous FTP server已經可以開始對外提供服務了，當然之後可以更進一步地研究如何架設一個regular user從自己的家目錄上傳或下載檔案。

補充:
如果你有開ufw(UncomplicatedFirewall)而且預設針對incoming traffic都是deny的話，記得加一下允許FTP連線的rule，例如:

$ sudo ufw allow from any to any port 20,21 proto tcp

(這邊暫時不考慮FTP PASV mode, 所以只需要開放TCP port 20,21) 

如何在Ubuntu 18.04 LTS開啟HWE(Hardware Enablement Stack)

簡單的說明一下我個人覺得HWE的主要用途:

透過HWE為現有的Ubuntu LTS版本(Desktop, Server, Cloud)提供了更新的Kernel和X來進一步支援新的硬體。比方說預設18.04 LTS是採用Kernel 4.15，然而透過HWE的機制，使用者可以在18.04 LTS跑Kernel 4.18(18.10預設內核)。

以下透過Ubuntu Server來實做一下:

1. 檢查系統是否有支援HWE:
root@server1 ~# hwe-support-status --verbose

2. 開啟HWE:
root@server1 ~# sudo apt install --install-recommends linux-generic-hwe-18.04

3. 確定Kernel可以透過HWE更新到4.18:

是不是很簡單呢？ :)

後記補充:
18.04.2 預設是安裝Kernel 4.18(Fresh install)，但如果想從既有的18.04升級到18.04.2，看起來Kernel還是會停留在4.15，所以如果需要新的Kernel或是新的drivers，可以考慮透過HWE來升級這些部份。

Ubuntu 14.04 LTS即將步入End of Life

還在使用Ubuntu 14.04 LTS的發行版本嗎? 但是14.04即將在2019/4/30步入End of Life囉~ 所以到時候就沒有辦法繼續讓14.04 LTS的機器可以享有最新版本的Linux Kernel或是應用軟體安全性相關的升級.

不過其實也不用太擔心啦! 一般用戶的話, 建議可以把14.04考慮升級成16.04或是18.04 LTS, 但如果是企業用戶還想停留在14.04操作環境的話其實可以考慮Canonical Ubuntu Advantage讓運行在企業裡面的Ubuntu 14.04 LTS將來持續有安全性更新.

至於如何將14.04升級到16.04或是18.04呢? 其實步驟很簡單, 可以參考以下的連結透過全圖形化介面就可以輕鬆升級:
https://tutorials.ubuntu.com/tutorial/tutorial-upgrading-ubuntu-desktop#0

順帶一提2019/3/6有個線上的session可以參考囉～
How to ensure the ongoing security compliance of Ubuntu 14.04 LTS ‘Trusty Tahr’

ThinkPad X1 Carbon 6th + Ubuntu 18.04 + LVFS

前言:

以往Linux的使用者如果要做BIOS或韌體升級的話，通常實作的方法有兩種:

1. 切換到Windows去執行廠商所提供的工具來升級。
2. 手動抓取相關的firmware然後自行製作開機disk來升級。

換句話說，其實對Linux使用者是挺不方便的，所以有人提出了LVFS project這個好主意。

LVFS(Linux Vendor Firmware Service)? 其實白話來說就是提供一個public pool然後邀請各家OEM/ODM廠商把自家最新的硬體firmware放上去，之後Linux系統便可以會透過fwupd這隻daemon去下載並且更新最新的firmware。

更多詳細的資訊可以參考LVFS的網站:

https://fwupd.org/users

以下是我擷取Ubunut 18.04在GNOME的畫面，可以看到我的X1有相關新firmware或是BIOS可以更新了。

所以如果Linux系統提醒你/妳可以升級BIOS的時候，也不用太訝異囉～ :D

Canonical Livepatch service

其實我沒接觸過Canonical Livepatch service，直到公司內部有同事在internal meeting裡面介紹後，我才發現到這個功能對於廣大的IT人員將會是一個非常好用的功能，而且某些程度上還可以減少些出錯的機會。

關於Canonical Livepatch service，我個人覺得它最主要的目的就是可以讓Linux kernel安裝上一些fixes但是系統不需要重新開機！而且kernel也不需要整個升級，相信對於一些系統必需保持在某個版本的kernel，或是不允許重新開機跟system downtime很要求的環境，這個功能確實是非常實用！

Canonical livepatch service其實在Ubuntu 14.04就開始支援了，但當時只支援CLI去配置Canonical livepatch service，不過從18.04之後，在GUI就可以很簡單的開啟以及使用它。

關於CLI如何使用，可以參考以下的連結：

https://blog.ubuntu.com/2017/06/06/canonical-kernel-livepatch-service-now-available-for-ubuntu-14-04-lts

https://www.ubuntu.com/livepatch 

GUI的話可以參考下面幾個步驟：
1. Software & Updates -> Updates.

2. 點選Sign in button.

3. 輸入你的Ubuntu SSO帳號(Ubuntu One account)。

4. 接著輸入Ubuntu 2 factor authentication。

如果順利的話，你可以看到Sing in button變成Sing Out，順便用CLI檢查一下。

所以當Sing in成功後，系統會從snap store自動安裝canonical-livepatch，相關的token也會自動抓取下來，比起14.04 or 16.04來說真的方便許多！

最後這邊要注意一下，Canonical livepatch service預設一組Ubuntu One帳號只允許3台機器使用，如果你是企業用戶的話，那可以考慮Ubuntu advantage來支援更多的機器。

在Ubuntu 18.04 架設VNC Server

很久前有筆記過如何在CentOS7上架設VNC Server，這幾天實做了一下VNC Server在Ubuntu 18.04上。

以下就簡單紀錄一下步驟。

Steps:
1. Install VNC Server (遠端桌面環境將採用xfce):

$ sudo apt-get install vnc4server xfce4 xfce4-goodies

2. 建立VNC server的配置檔與user密碼:

$ vncpasswd

$ vim.tiny ~/.vnc/xstartup

#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
exec startxfce4 

$ chmod 755 ~/.vnc/xstartup

3. 手動啟動VNC Server:

這個時候我們先測試看看VNC Server可不可以正常工作。

如果有看到以上類似的畫面，那說明VNC Server已經啟動並且listen在TCP port 5901。但是請注意，預設它會只listen在localhost，這個等一下在建立systemd startup script的時候，我們可以修改它。

4. 建立systemd startup script: 

 做這個設定的最大好處是將來系統重開機後，我就不需要每次都要手動啟動VNC Server了。

4.1 建立VNC Server script file:

 $ sudo vim.tiny /etc/systemd/system/vncserver@.service

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=simple
User=u
PAMName=login
PIDFile=/home/%u/.vnc/%H%i.pid
ExecStartPre=/bin/sh -c '/usr/bin/vncserver -localhost no -kill :%i > /dev/null 2>&1 || :'
ExecStart=/usr/bin/vncserver :%i -localhost no -geometry 1440x900 -alwaysshared -fg
ExecStop=/usr/bin/vncserver -kill :%i

[Install]
WantedBy=multi-user.target

剛剛有提到預設VNC Server只會listen在localhost:5901，但透過參數-localhost no可以讓它listen在0.0.0.0也就是all net的概念。 

4.2 手動reload systemd: (每次有新增或修改systemd的startup script file後，記得此步驟)

$ sudo systemctl daemon-reload

4.3 透過systemd啟動VNC Server:

$ sudo systemctl start vncserver@1.service

4.4 在系統開機時，自動啟動VNC Server:

$ sudo systemctl enable vncserver@1.service

假設一切順利的話，輸入相關的命令後，應該可以看到類似的畫面。

 5. 遠端測試: (採用Ubuntu內建的Remmina remote desktop client)

2018 Top 10的Snap 套件

即將邁入2019，回顧一下2018 前10名最受喜愛的snap套件是哪些呢？

剛看了一下敝公司的官方網頁，以下有Top10的排行榜唷～ :D
https://blog.ubuntu.com/2018/12/27/top-snaps-in-2018

不過說真的，我個人蠻常用的Skype, mailspring, simplenote現在都用snap來安裝，並且會自動定時更新，超方便的呀～

不知道何時會有line for snap?

How can I setup an IPv6 router via radvd on Ubuntu 18.04 LTS?

What's radvd?
Router advertisement daemon.

Reference:
https://zh.wikipedia.org/wiki/Radvd
http://www.litech.org/radvd/

一般來說 IPv6 Client決定Global IPv6的方式有兩種，分別是Stateless與Stateful，預設radvd是採用stateless IPv6，不過透過更改某個參數(M flag)，就可以轉換成stateful，但是此時網路上必須有對應的DHCPv6 server來負責管理與分配IPv6 address。

網路上可以找到很多先進寫的資料關於Stateless與Stateful的差異，我也就不班門弄斧了，廢話不多說，直接進入主題，如何架設radvd在Canonical/Ubuntu 18.04 LTS。

Steps:

Step1. Install radvd package.

$ sudo apt-get install radvd

Step2. Copy example file of radvid.conf from /usr/share/doc/radvd/examples/ to /etc.

$ sudo cp /usr/share/doc/radvd/examples/radvd.conf.example /etc/radvd.conf

Step3. Open/Edit radvd.conf

根據你的需求，去配置相關的參數，最重要的應該是prefix，更多詳細的參數可以參考man page。

https://www.systutorials.com/docs/linux/man/5-radvd.conf/

Step4. Restart radvd

$ sudo systemctl restart radvd; sudo systemctl enable radvd

以上一個簡單的IPv6 stateless的Router已經架設完成，IPv6 client現在自己可以搭配prefix自動產生host ID。

How can I configure Ubuntu 16 to start teamviewer automatically?

Steps:

1. Opened /etc/init.d/rc.local

$ sudo vi /etc/init.d/rc.local

2. Added teamviewer's command and parameter below in file rc.local:

teamviewer passwd ubuntu

3. Restart system

4. Examine if teamviewer daemon can work as expected:

$ systemctl status teamviewerd
● teamviewerd.service - TeamViewer remote control daemon
   Loaded: loaded (/etc/systemd/system/teamviewerd.service; enabled; vendor preset: enabled)
   Active: active (running) since 三 2018-08-15 11:00:14 CST; 1min 25s ago
  Process: 1555 ExecStart=/opt/teamviewer/tv_bin/teamviewerd -d (code=exited, status=0/SUCCESS)
 Main PID: 1567 (teamviewerd)
   CGroup: /system.slice/teamviewerd.service
           └─1567 /opt/teamviewer/tv_bin/teamviewerd -d

$ ps aux | grep -i teamviewer
root      1567  0.3  0.3 1181612 12212 ?       Sl   11:00   0:00 /opt/teamviewer/tv_bin/teamviewerd -d
u         1890  0.3  2.2 1990224 88556 ?       Sl   11:00   0:00 /opt/teamviewer/tv_bin/TeamViewer

Afterwards, you can remote control host via Partner ID and password which is ubuntu in this example.

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)

How can I setup a Linux NAT Router in Ubuntu?

Steps:

1. Enable packet forwarding for IPv4 between NICs:

• Open and edit /etc/sysctl.conf
• Ucomment net.ipv4.ip_forward=1
• To execute command sysctl -p

2. Create a postrouting rule within iptables:

• iptables -t nat -A POSTROUTING -o enp0s8 -s 192.168.1.0/24 -j MASQUERADE
• Where enp0s8 is WAN and 192.168.1.0/24 is LAN, please modify those parameters depend on your environment.

3. Save and restore iptables rule after reboot:

• Save rules: iptables-save > /etc/iptables.save
• Restore rules:
• Open and edit /etc/network/interfaces to add pre-up.....

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
auto enp0s3
iface enp0s3 inet static
address 192.168.1.254
netmask 255.255.255.0
pre-up iptables-restore < /etc/iptables.save

Done~

如何在Ubuntu 16.04 desktop 透過PXE安裝Ubuntu?

在開始之前，請先準備與安裝相關的service在Ubuntu desktop 16.04 LTS:

準備：
1. Download Ubuntu desktop ISO
2. Download PXE bootloader

安裝：
1. DHCP Server

$ sudo apt-get install isc-dhcp-server

2. TFTP Server

$ sudo apt-get install tftpd-hpa inetutils-inetd

3. NFS Server

$ sudo apt-get install nfs-kernel-server

配置：
1. DHCP Server:

$ sudo vi /etc/dhcp/dhcpd.conf

 subnet 192.168.1.0 netmask 255.255.255.0 {
 range 192.168.1.200 192.168.1.253;
 option domain-name-servers 8.8.8.8;
 option routers 192.168.1.1;
 option broadcast-address 192.168.1.255;
 default-lease-time 600;
 max-lease-time 7200;
 next-server 192.168.1.254;
 filename "pxelinux.0";
 }

 $ sudo systemctl restart isc-dhcp-server

 2. TFTP Server:

$ sudo vi /etc/default/tftpd-hpa

TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/var/lib/tftpboot"TFTP_ADDRESS=":69"
TFTP_OPTIONS="--secure"
RUN_DAEMON="yes"
OPTIONS="-l -s /var/lib/tftpboot"

$ sudo vi /etc/xinetd.conf

tftp    dgram   udp    wait    root    /usr/sbin/in.tftpd /usr/sbin/in.tftpd -s /var/lib/tftpboot

$ sudo systemctl restart tftpd-hpa 

3. PXE bootloader:

$ tar -xJf syslinux-6.03.tar.xz
$ cd syslinux-6.03
$ sudo cp bios/core/pxelinux.0 /var/lib/tftpboot
$ sudo cp bios/com32/lib/libcom32.c32 /var/lib/tftpboot
$ sudo cp bios/com32/libutil/libutil.c32 /var/lib/tftpboot
$ sudo cp bios/com32/elflink/ldlinux/ldlinux.c32 /var/lib/tftpboot
$ sudo cp bios/com32/menu/vesamenu.c32 /var/lib/tftpboot
$ mkdir /var/lib/tftpboot/pxelinux.cfg
$ sudo vi /var/lib/tftpboot/
pxelinux.cfg/default 

DEFAULT vesamenu.c32
MENU TITLE Network boot
LABEL ubuntu-mate-16.04.2-desktop-amd64
  MENU LABEL ubuntu-mate-16.04.2-desktop-amd64
  KERNEL vmlinuz.efi
  APPEND initrd=initrd.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.254:/var/nfs/ubuntu_desktop splash -- 

* Remember to copy vmlinuz.efi and initrd.lz to the folder /var/lib/tftpboot from Ubuntu ISO.
* 補充: 針對18.04要修改一下設定檔如下:
  APPEND initrd=./u18/initrd_ubuntu18.04.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.254:/var/nfs/ubuntu18.04 splash toram --

4. NFS file Server:

$ sudo mount -o loop ubuntu-16.04.3-desktop-amd64.iso /mnt/
$ sudo mkdir -p /var/nfs/ubuntu_desktop
$ sudo cp -rf /mnt/* /var/nfs/ubuntu_desktop/
$ sudo vi /etc/exports
/var/nfs/ubuntu_desktop *(ro,sync)

$ sudo systemctl restart nfs-kernel-server

$ showmount -e localhost 

Export list for localhost:
/var/nfs/ubuntu_desktop *

Boot from Network boot:

Done!

How can I move Launcher from left to the buttom on Ubuntu 16.04?

It's very simple, and it works for me even if I reboot or re-login the system b/c Ubuntu will remember it.

Steps:
1. Open a terminal

2. To execute "gsettings set com.canonical.Unity.Launcher launcher-position Bottom"

Done~

How can I get detail information of USB device?

The command lsusb, which able to list all USB devices of machine below:

lawrence@Lawrence-ThinkPad-X200:~$ lsusb
Bus 002 Device 004: ID 7392:7711 Edimax Technology Co., Ltd EW-7711UTn nLite Wireless Adapter [Ralink RT2870]
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 17ef:480c Lenovo Integrated Webcam
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 002: ID 08ff:2810 AuthenTec, Inc. AES2810
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

However, I would like to know more informations. For example, speed, vendor, manufacturer......, etc. And there is a command usb-devices, which can help me.

lawrence@Lawrence-ThinkPad-X200:~$ usb-devices 

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  4 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=7392 ProdID=7711 Rev=01.01
S:  Manufacturer=RalinkS:  Product=802.11 n WLAN
S:  SerialNumber=1.0
C:  #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=450mA
I:  If#= 0 Alt= 0 #EPs= 7 Cls=ff(vend.) Sub=ff Prot=ff Driver=rt2800usb

T:  Bus=04 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=5000 MxCh= 2
D:  Ver= 3.00 Cls=09(hub  ) Sub=00 Prot=03 MxPS= 9 #Cfgs=  1
P:  Vendor=1d6b ProdID=0003 Rev=04.13
S:  Manufacturer=Linux 4.13.0-32-generic xhci-hcd
S:  Product=xHCI Host Controller
S:  SerialNumber=0000:0d:00.0
C:  #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=0mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub

Above you can see the Spd=480/USB 2.0, and Spd=5000/USB 3.0.

[Shell script] Find user in system

The first way:

#!/bin/bash

if [ $# -eq 0 ]
then
 echo "Usage: $0 lawrence"
else
  grep "\<$1\>" /etc/passwd > /dev/null
  RETVAL=$?
  if [ $RETVAL -eq 0 ]
  then
   echo "Username $1 was found in the system"
  else
   echo "Cannot find username $1"
 fi
fi

The second way:

[ $# -eq 0 ] &&  { echo "Usage: $0 lawrence" ; exit 1; }

grep "\<$1\>" /etc/passwd > /dev/null
RETVAL=$?

[ $RETVAL -eq 0 ] && echo "Username $1 was found in the system" || echo "Cannot find username $1"

How can I add EPEL reop on CentOS 7.x?

It's quite simple, just two commands below:

# yum install epel-release

# yum repolist

Sample output:

How can I disable dnsmasq listen port 53 on the Ubuntu 16.04 LTS?

By default the DNS Server of Ubuntu 16.04 LTS will be 127.0.0.1:53, i.e., localhost.




Therefore, system will forward DNS query to the localhost first, and forward to the DNS server which obtained from the DHCP server afterward.

Actually, I didn't prefer this method, so that I would like to turn off  this mechanism via steps were listed below:

Steps:
1. Open /etc/NetworkManager/NetworkManager.conf

2. To disable dnsmasq


3. Restart NetworkManager


4. Examine /etc/resolv.conf


Done.