Ubuntu¶
Info
Most notes on this page are based on my Ubuntu laptop.
- 20.04: 2021-09-12 -> Now.
- 18.04: 2020-04-12 -> 2021-09-12.
- 16.04: ~ -> 2020-04-12
- 14.04: ~ -> ~
Package Manager¶
Advanced Package Tool (APT)¶
APT is a package management system for Debian and other Linux distributions based on it, such as Ubuntu.
PPA¶
PPAs (Personal Package Archive) are repositories hosted on Launchpad. You can use PPAs to install or upgrade packages that are not available in the official Ubuntu repositories.
see also:
proxy for apt
proxychains seems not work well before sudo or after sudo, and I don’t want to add a system proxy permanently, then I found a temporary way,
sudo http_proxy='http://user:pass@proxy.example.com:8080/' apt-get install package-name
refer to how to install packages with apt-get on a system connected via proxy?
dpkg (Debian Package Manager)¶
“dpkg works under the hood of APT. While APT manages remote repositories and resolves dependencies for you, it use dpkg to actually make the changes of installing/removing package.”
- list installed packages:
dpkg -l- flag ‘ii’ (installed) and ‘rc’ (removed but configuration), refer to for more details
- flag ‘ii’ (installed) and ‘rc’ (removed but configuration), refer to
Snap¶
snaps: the packagessnapd: the tool for using packages
Snaps are self-contained applications running in a sandbox with mediated access to the host system.
- list all installed packages:
$ date
Sat 11 Jun 2022 08:22:05 PM CST
$ snap list
Name Version Rev Tracking Publisher Notes
bare 1.0 5 latest/stable canonical✓ base
canonical-livepatch 10.2.3 146 latest/stable canonical✓ -
core 16-2.56 13308 latest/stable canonical✓ core
core18 20220428 2409 latest/stable canonical✓ base
gnome-3-28-1804 3.28.0-19-g98f9e67.98f9e67 161 latest/stable canonical✓ -
gtk-common-themes 0.1-79-ga83e90c 1534 latest/stable canonical✓ -
kde-frameworks-5 5.47.0 27 latest/stable kde✓ -
kde-frameworks-5-core18 5.61.0 32 latest/stable kde✓ -
kde-frameworks-5-qt-5-14-core18 5.68.0 4 latest/stable kde✓ -
ksnip 1.10.0 443 latest/stable dporobic -
- check available updates
# without refreshing
$ snap refresh --list
# perform refreshing
$ sudo snap refresh
- check info of packages
$ snap info <snap name>
see also:
Battery¶
Charge Battery Adaptively
Check the post.
Disk¶
Extend Disk
一直想扩容来着，但总是下不了决心。今天决定了，参考 google 搜索“Ubuntu 扩容”的前几条结果，便开始干了。
- 采用启动 U 盘，因为根目录在使用状态，幸好启动 U 盘还在。
- 使用 Gparted 时有个大大的 warning，说对含 /boot 分区的硬盘进行操作可能会不能正常启动，有点吓到了，最后还是狠下心继续下去了。
- 网上有人说，不要用 Gparted 对 Windows 进行压缩，而应该在 Windows 中进行压缩，可是此时已经开始了，想中断但怕造成更严重的后果，幸好最后启动 Windows 时只是多了步检查硬盘，并没有不能启动的状况。
中间提心吊胆，好在最后顺利扩容完成。
see also: Why are there so many different ways to measure disk usage? - Unix & Linux Stack Exchange
Portable SSD
Check the post
Clean disk space
- autoremove
apt autoremove --purge - manually find unused packages:
dpkg -landapt list --installed - for anaconda, run
conda clean -a
Mount with Options
By default, the Segate disk would return owner as root.
Use
sudo umount /dev/XXX
sudo mount -o rw,user,uid=1000,dmask=007,fmask=117 /dev/XXX /media/weiya/Segate
where the first step might throw busy error, and the processes use the disk can be found via
fuser -cu /local/mnt/
ps -ef | grep XXX
refer to
GNOME¶
GNOME (originally an acronym for GNU Network Object Model Environment) is a desktop environment for Unix-like operating systems.
The version on my T460p is 3.28.2, which can be seen from About.
GNOME Shell¶
GNOME Shell is the graphical shell of the GNOME desktop environment. It provides basic functions like launching applications, switching between windows and is also a widget engine. . User interface elements provided by GNOME Shell include the Panel at the top of the screen, the Activities Overview, and Message Tray at the bottom of the screen.
The version on my T460p is
$ gnome-shell --version
GNOME Shell 3.28.4
GNOME Shell Extensions¶
GNOME Shell Extensions are small pieces of code written by third party developers that modify the way GNOME works. They are similar to Chrome Extensions or Firefox Addons. We can install the extensions via extensions.gnome.org in Firefox. After installation, we can disable or enable, or even configure on such website, alternatively, we can use gnome-tweaks to control them.
Lunar Date¶
Here is a plugin to show Chinese Lunar Date: Lunar Calendar 农历. Since here are some latest comments, I guess it would be OK.
However, the first installation attempt failed, it shows ERROR. Then I realized that I might need to install the dependency mentioned in the plugin page,
sudo apt install gir1.2-lunar-date-2.0
Then reinstall the plugin, it succeed! But interestingly, the Chinese characters are shown as Pinyin (see the following left image)
| Before | After |
|---|---|
 |
 |
Then I found the same issue in an older post
A solution is
@GuanGGuanG
copy
/usr/share/locale/zh_CN/LC_MESSAGES/liblunar.mo
to
/usr/share/locale/en/LC_MESSAGES/
就可以在英文环境下正常显示了
Although no found liblunar.mo, there is
$ pwd
/usr/share/locale/zh_CN/LC_MESSAGES
$ ll | grep lunar
-rw-r--r-- 1 root root 4746 Nov 12 2016 lunar-date.mo
then
$ sudo cp lunar-date.mo ../../en/LC_MESSAGES/
It cannot take effects immediately, the natural way is to reboot. But currently I do not want to reboot, and then I tried to reinstall the plugin in Firefox, but not work.
Then I tried to reload locale since the modification seems related to locale, so I found this answer and tried
$ . /etc/default/locale
but not work.
Then I realized that it might be necessary to reload GNOME Shell, so I found How to restart GNOME Shell from command line?, and tried
$ gnome-shell --replace &
It works, as shown in the above right figure. A minor side change is that the English colon in the time 14:37 seems to change to the Chinese colon.
System Monitor¶
通过 gnome-shell extension: gnome-shell-system-monitor-applet 实现
不过目前有个小问题，字体略小，尝试通过 gnome-tweaks 中的 scaling 来改变字体大小，但似乎对这些字体仍不适用，先将就用着吧。
unblack lock screen¶
按 Win+L 锁屏后，很快就直接变黑了。因为感觉屏保还挺好看的，所以并不想直接黑屏。参考 GNOME3锁屏和锁屏后，如何设置屏幕常亮？ - Eglinux的回答 - 知乎，安装 Unblank lock screen.
更简单的技巧是长按 Win+L，似乎确实不会直接黑屏，然后会直接采用设置的关屏时间（Setting > Power），参考 GNOME3锁屏和锁屏后，如何设置屏幕常亮？ - dale的回答 - 知乎。
sound device chooser¶
tried but not good. Sound Input & Output Device Chooser
Filesystem¶
File Permissions¶
采用ls -l 便可以查看文件(夹)权限，比如
-rw-rw-r-- 1 weiya weiya 137969 3月 8 2017 font.txt
-rw-r--r-- 1 root root 35792 12月 26 23:50 geckodriver.log
-rw-r--r-- 1 root root 327350 12月 27 01:38 ghostdriver.log
- 文件类型和文件权限
- 文件类型由第一个字母表示，常见的有
d(目录)，-(文件)，l(链接) - 权限分为三段，每三个字符一段，分别表示，文件所有者u、文件所属组g、其他用户o对该文件的权限，其中r: 可读，等于 4w: 可写，等于 2x: 可执行，等于 1-: 无权限，等于 0s: set user or group ID on execution (s)X: execute/search only if the file is a directory or already has execute permission for some usert: restricted deletion flag or sticky bit
- 文件链接个数
- 文件所有者
- 文件所在群组
- 文件长度
- 时间
- 文件名称
采用chmod修改权限（参考http://www.linuxidc.com/Linux/2015-03/114695.htm），如
chmod -R 700 Document/
chmod -R [ugoa...][[+-=][perms...]] # refer to `man chmod` for more details
其中 -R 表示递归，perms 为上述 rwxXst，而 a 表示所有用户，即 ugo.
采用 chown 改变所有者，比如
chown -R username:users Document/
chmod g+s . 会使得当前文件夹 . 中所有新建文件或文件夹都继承 . 的 group，而不是创建者所属的 group，所以这一般配合 chgrp 使用。参考 ‘chmod g+s’ command
Modify vs Change¶
在找学习资料时，突然不是很确定当初是否已经在用这台笔记本了，所以想确定一下本机的装机时间，参考 How can I tell what date Ubuntu was installed?，主要时通过查看文件的上次修改时间，比如
$ ls -lt /var/log/installer/
total 1200
-rw-rw-r-- 1 root root 464905 Dec 2 2016 initial-status.gz
-rw-r--r-- 1 root root 60 Dec 2 2016 media-info
-rw------- 1 syslog adm 334743 Dec 2 2016 syslog
-rw------- 1 root root 2467 Dec 2 2016 debug
-rw------- 1 root root 407422 Dec 2 2016 partman
-rw------- 1 root root 17 Dec 2 2016 version
-rw------- 1 root root 956 Dec 2 2016 casper.log
又如
$ ls -lt /
...
drwxrwxr-x 2 root root 4096 Dec 2 2016 cdrom
drwx------ 2 root root 16384 Dec 2 2016 lost+found
drwxr-xr-x 2 root root 4096 Apr 21 2016 srv
出现了 2016.04.21 的一条记录。但如果我加上 -c，结果竟然不一样
$ ls -clt /
...
drwxrwxr-x 2 root root 4096 Dec 2 2016 cdrom
drwxr-xr-x 2 root root 4096 Dec 2 2016 srv
drwx------ 2 root root 16384 Dec 2 2016 lost+found
难道 ls 默认显示的时间不是上次修改时间吗？？另外注意到 srv 其实是一个空文件夹。
这时我用 stat 进一步查看，
$ stat /srv
File: /srv
Size: 4096 Blocks: 8 IO Block: 4096 directory
Device: 825h/2085d Inode: 1179649 Links: 2
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2021-05-05 08:43:20.955106697 +0800
Modify: 2016-04-21 06:07:49.000000000 +0800
Change: 2016-12-02 02:46:47.363728274 +0800
Birth: -
发现有两个修改时间，Modify 和 Change，两者区别在于
Modify: the last time the file was modified (content has been modified)Change: the last time meta data of the file was changed (e.g. permissions)
然后进一步查看 Windows 系统的时间，
$ ll -clt
...
drwxrwxrwx 1 weiya weiya 4096 Oct 1 2016 '$Recycle.Bin'/
drwxrwxrwx 1 weiya weiya 0 Sep 29 2016 FFOutput/
-rwxrwxrwx 2 weiya weiya 15151172 Jul 2 2016 WindowsDENGL.tt2*
-rwxrwxrwx 2 weiya weiya 16092228 Jul 2 2016 WindowsDENG.tt2*
-rwxrwxrwx 2 weiya weiya 16217976 Jul 2 2016 WindowsDENGB.tt2*
-rwxrwxrwx 1 weiya weiya 400228 Mar 19 2016 bootmgr*
-rwxrwxrwx 1 weiya weiya 1 Mar 19 2016 BOOTNXT*
drwxrwxrwx 1 weiya weiya 8192 Mar 18 2016 Boot/
最早可以追溯到 2016.03.18.
.fuse_hidden¶
I found a file res/res_monodecomp/.fuse_hidden0016fbd000000001, which is “a file was deleted but there is at least one software which is still using it, so it cannot be removed permanently” . And it is suggested to use lsof to determine the application that uses such file. However,
$ lsof ./res/res_monodecomp/
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
Output information may be incomplete.
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/129/gvfs
Output information may be incomplete.
/run/user/1000¶
Info
Post: 2022-04-05 09:58:32
Checking the usage of disk by df -h, here is a line,
Filesystem Size Used Avail Use% Mounted on
tmpfs 2.0G 24K 2.0G 1% /run/user/129
tmpfs 2.0G 192K 2.0G 1% /run/user/1000
where
tmpfs(short for Temporary File System) is a temporary file storage paradigm implemented in many Unix-like operating systems. It is intended to appear as a mounted file system, but data is stored in volatile memory instead of a persistent storage device./run/user/$uidis created by pam_systemd and used for storing files used by running processes for that user.
100% snap /dev/loop¶
$ df -h
/dev/loop1 9.0M 9.0M 0 100% /snap/canonical-livepatch/138
/dev/loop2 9.0M 9.0M 0 100% /snap/canonical-livepatch/146
/dev/loop3 114M 114M 0 100% /snap/core/13308
/dev/loop0 128K 128K 0 100% /snap/bare/5
“Having Snap images which consume 100% of their filesystem is perfectly acceptable” and “it’s supposed to work that way”, refer to
See also: What is /dev/loopx?.
Birth time¶
Info
Post: 2023-03-06 17:23:57 -0500
有一篇博客写了草稿未 commit，然后匆忙更改后想知道上一次写作的时间。但是 stat 与 ls 中 Birth 字段为空。
首先尝试了 debugfs，但似乎这对于 ext4 有用。
$ sudo debugfs -R 'stat 451072' /dev/sdc1
debugfs 1.45.5 (07-Jan-2020)
debugfs: Bad magic number in super-block while trying to open /dev/sdc1
/dev/sdc1 contains a ntfs file system labelled 'Seagate Backup Plus Drive'
stat: Filesystem not open
对于 ntfs，找到了这个,
$ getfattr --only-values -n system.ntfs_crtime_be four-generations-under-one-roof.md |
perl -MPOSIX -0777 -ne '$t = unpack("Q>"); print ctime $t/10000000-11644473600'
Sun Feb 26 22:52:09 2023
其中 11644473600 是 Windows 的开始计时时间点 (1601-01-01T00:00:00Z) 与 Linux 计时开始点 (1970-01-01T00:00:00Z) 所差的秒数（）。
Font¶
fc-list¶
view installed fonts
# only print the font-family
$ fc-list : family
# add language selector
$ fc-list : family lang=zh
...
Fira Sans,Fira Sans UltraLight
Fira Sans,Fira Sans Light
Noto Serif CJK KR,Noto Serif CJK KR ExtraLight
# with format option, get the family names of all the fonts (note that the above family also specify the detailed style)
$ fc-list --format='%{family[0]}\n' :lang=zh | sort | uniq
...
文泉驿等宽微米黑
文泉驿等宽正黑
新宋体
refer to fc-list command in Linux with examples
Install Local Fonts¶
霞鹜文楷
https://github.com/lxgw/LxgwWenKai
git clone git@github.com:lxgw/LxgwWenKai.git
cp LxgwWenKai/fonts/TTF/* ~/.local/share/fonts/
仿宋 & 黑体
以安装仿宋和黑体为例，这是本科毕业论文模板所需要的字体，字体文件已打包
$ wget -c https://sourceforge.net/projects/zjuthesis/files/fonts.tar.gz/download -O fonts.tar.gz
$ tar xvzf fonts.tar.gz
fonts/STFANGSO.TTF
fonts/
fonts/simhei.ttf
$ sudo mkdir -p /usr/share/fonts/truetype/custom/
$ sudo mv fonts/* /usr/share/fonts/truetype/custom/
$ sudo fc-cache -f -v
NOTE: 除了系统的字体目录，也可以选择用户目录，”~/.local/share/fonts/”. 另见 另外 fc-cache 也不是必须的。
安装完成后，
$ fc-list :lang=zh
/usr/share/fonts/truetype/custom/simhei.ttf: SimHei,黑体:style=Regular,Normal,obyčejné,Standard,Κανονικά,Normaali,Normál,Normale,Standaard,Normalny,Обычный,Normálne,Navadno,Arrunta
/usr/share/fonts/truetype/custom/STFANGSO.TTF: STFangsong,华文仿宋:style=Regular
Font Name in xeCJK
在 \setCJKmainfont{} 中使用 fc-list 冒号之前的字体名。也可以使用字体文件，但需要指定具体路径，否则只会在当前目录下寻找。
Some Free Fonts¶
Headphone¶
The output candidates are
- HDMI/DisplayPort - Built-in Audio
- Speakers - Built-in Audio
- Headphone - LE-Bose QC35 II
and there are two profiles for Headphone
- High Fidelity Playback (A2DP Sink)
- Headset Head Unit (HSP/HFP)
also two profiles for Speakers
- Analog Stereo Output
- Analog Surround 4.0 Output
and one profile for HDMI/DisplayPort
- Digital Stereo (HDMI) Output
There are two devices for sound input
- Internal Microphone - Built-in Audio
- Bluetooth Input - LE-Bose QC35 II
Here are some observations
- The profile
High Fidelity Playbackis much more confortable than another profile. - If
Output = Headphone + High Fidelity, thenInputcannot be set asBluetooth Input - Otherwise, if set
InputasBluetooth Input, then the Profile ofOutputwould become toHeadset Head Unit
Sometimes, no sound from the headphone, and possibly the headphone is connected to another device. Refer to Using multiple Bluetooth® connections for switching the connected devices for the headphone.
When two devices are actively connected, you can play music from either device. To switch between connected devices, pause the first device and play music from the second.
But sometimes either devices are playing sound, a less elegant way is to disconnect other devices.
see also Pair Bose QuietComfort 35 with Ubuntu over Bluetooth - Ask Ubuntu
Turn on/off Bluebooth from CLI
某次，合上笔记本盖子然后打开后，找不到蓝牙，而且在设置界面中也无法打开蓝牙。
rfkill block bluetooth
rfkill unblock bluetooth
always a2dp_sink!
Sometimes it is noisy, and annoying “call from”. This is due to the profile, but using the GUI to change it seems not work. So try to work from the command line.
# list available cards
$ pacmd list-cards
profiles:
headset_head_unit: Headset Head Unit (HSP/HFP) (priority 30, available: unknown)
a2dp_sink: High Fidelity Playback (A2DP Sink) (priority 40, available: yes)
off: Off (priority 0, available: yes)
active profile: <a2dp_sink>
headset_head_unit, it would be noisy. Tried
pacmd set-card-profile <card name> a2dp_sink
However, after reconnecting, it works well, and it can easily switch between headset_head_unit and a2dp_sink.
See also: and
Nvidia Driver¶
Install via the GUI Software & Updates. If succeed, then
$ nvidia-smi
can display the GPU memory usage, together with the versions of driver and CUDA,
$ nvidia-smi
Mon Aug 2 22:08:19 2021
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 460.91.03 Driver Version: 460.91.03 CUDA Version: 11.2 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
| | | MIG M. |
|===============================+======================+======================|
| 0 GeForce 940MX Off | 00000000:02:00.0 Off | N/A |
| N/A 63C P0 N/A / N/A | 724MiB / 2004MiB | 9% Default |
| | | N/A |
+-------------------------------+----------------------+----------------------+
+-----------------------------------------------------------------------------+
| Processes: |
| GPU GI CI PID Type Process name GPU Memory |
| ID ID Usage |
|=============================================================================|
| 0 N/A N/A 400 G WeChatWeb.exe 9MiB |
| 0 N/A N/A 663 G ...cent\WeChat\WeChatApp.exe 7MiB |
| 0 N/A N/A 4454 G ...AAAAAAAAA= --shared-files 59MiB |
| 0 N/A N/A 7440 G /usr/lib/xorg/Xorg 437MiB |
refer to Linux安装NVIDIA显卡驱动的正确姿势 for other approaches (seems more technical).
Different CUDA version shown by nvcc and NVIDIA-smi
refer to Different CUDA versions shown by nvcc and NVIDIA-smi
CUDA has 2 primary APIs, the runtime and the driver API. Both have a corresponding version
- The necessary support for the driver API (e.g. libcuda.so on linux) is installed by the GPU driver installer.
- The necessary support for the runtime API (e.g. libcudart.so on linux, and also nvcc) is installed by the CUDA toolkit installer (which may also have a GPU driver installer bundled in it).
nvidia-smi: installed by the GPU driver installer, and generally has the GPU driver in view, not anything installed by the CUDA toolkit installer.
nvcc: the CUDA compiler-driver tool that is installed with the CUDA toolkit, will always report the CUDA runtime version that it was built to recognize.
Kernel¶
Printer¶
Use Department Printer¶
The department printer is only accessible from the office PC, but request to switch the cable from office PC to my laptop, I can configure to use the printer from my laptop. The steps are
- choose LPD/LPR Host or Printer
- set host as
hpm605dn1.sta.cuhk.edu.hk
The detailed settings are
finally, the test page can be successfully printed,
If we forget the hostname, actually we can get the ip address from the panel of printer,
| step 1 | step 2 |
|---|---|
 |
 |
We can validate the hostname and the ip point to the same machine,
weiya@stapc220:~$ ping hpm605dn1.sta.cuhk.edu.hk
PING hpm605dn1.sta.cuhk.edu.hk (172.16.37.238) 56(84) bytes of data.
Share Printer¶
现有台 HP-Deskjet-1050-J410-series 打印机，通过 USB 接口。直接连接在 Ubuntu 上是可以实现打印功能的，现在想贡献给局域网内的其他设备，参考 使用Linux共享打印机，主要步骤为
- 安装 CUPS 服务，
sudo apt-get install cups并启动，sudo service cups start - 在
127.0.0.1:631的Administration >> Advanced勾选Allow printing from the Internet，并保存。 - 打开防火墙，
sudo ufw allow 631/tcp
在同一局域网内的 Windows 设备中，添加该打印机，地址即为Ubuntu中浏览器的地址，注意将 127.0.0.1 换成局域网 ip。如果顺利的话，添加后需要添加驱动程序，可以在 HP 官网下载。
Add Virtual Memory¶
通过交换文件实现
# 创建大小为2G的文件swapfile
dd if=/dev/zero of=/mnt/swapfile bs=1M count=2048
# 格式化
mkswap /mnt/swapfile
# 挂载
swapon /mnt/swapfile
注意文件应为 root:root，否则会提示
insecure file owner 1000, 0 (root) suggested.
另见 How to Resolve the Insecure warning in Swapon?
为了保证开机自动加载，在 /etc/fstab 加入
/mnt/swapfile swap swap defaults 0 0
具体每一列的含义可以通过 man fstab 查看。
挂载成功后就可以通过 free -h 查看内存情况。
swapfile on PSSD
如果 swapfile 在外接移动硬盘上，则开机时需要提前插好外接硬盘。否则会卡在开机那一步。反之，如果为了追求便携性不依赖于移动硬盘，则最后不要在移动硬盘中创建 swapfile.
这个方法也可以解决 “virtual memory exhausted: Cannot allocate memory” 的问题。
调整 swapiness，默认值为 60，
$ cat /proc/sys/vm/swappiness
越高表示越积极使用 swap 空间。
临时性使用
$ sudo sysctl vm.swappiness=80
参考 linux系统swappiness参数在内存与交换分区间优化
WiFi¶
Info
Post: 2022-04-01 23:57:09
校园网突然无法打开微信图片，公众号文章也无法加载，无法 ping 通 mp.weixin.qq.com，但在服务器上可以。所以第一个自然想法是利用动态转发搭建隧道，即在本地端运行
$ ssh -D 30002 server
然后便可以通过 socks5://127.0.0.1:30002 进行代理。加了代理之后，首先能够在浏览器端打开公众号文章。但想要微信本身也进行代理，并不直接，可能因为 wine 套壳的原因，后来也没有继续细究。
另一种方式便是换 wifi。除了 CUHK1x，也可以使用 eduroam，点击连接时，竟然发现连接状态下的 security 是哈佛帐号，然而我并没有利用哈佛帐号连接过 eduroam，而且帐号早已失效。其原因，很可能就是因为当时连接 Harvard Secure 时，会下载一个 JoinNow，并在本地运行 。
而此时所连接的 eduroam 中 security 便指向 joinnow 的两个密钥文件，
~/.joinnow/tls-client-certs$ ls
sw2-joinnow-client-cert-**************.crt
sw2-joinnow-client-cert-**************.p12
不过在该 wifi 下，不能直接访问服务器。于是想切换到学校帐号的 eduroam，但又想保留当前 profile。所以尝试直接复制 wifi profile 文件，
/etc/NetworkManager/system-connections$ sudo cp A B
然后修改每个 profile 的细节，注意 uuid 也必须修改，运行 uuid 生成，不然会视为同一个连接。修改完成后重启网络服务，
sudo systemctl restart NetworkManager
参考
另外，命令行操作进行网络连接详见 https://www.makeuseof.com/connect-to-wifi-with-nmcli/
Delete Hotspot¶
升级到 Ubuntu 18.04 后，开机自动连接到 Hotspot，每次需要手动禁止并改成 Wifi 连接，这个可以直接删除保存好的 Hotspot 连接
cd /etc/NetworkManager/system-connections/
sudo rm Hotspot
参考 How to remove access point from saved list
WiFi Hotpot (16.04)¶
Refer to
- 3 Ways to Create Wifi Hotspot in Ubuntu 14.04 (Android Support)
- How do I create a WiFi hotspot sharing wireless internet connection (single adapter)?
几处不同：
- 选择
mode时，直接选择hotpot即可，后面也无需更改文件 - 设置密码时位数不能少于 8 位
- 连接 WiFi 时 似乎需要 enable wifi。
Keyboard¶
实验室有一支 IKBC CD 87T 蓝牙键盘，于是便想试试。
- 连接：详见说明书
- Win 键失效：尝试按
Fn + Right Win及左Fn + Left Win，参考 IKBC键盘Win键失效的解决办法
1m_ipv4_udp_receive_buffer_errors¶
Info
The raw records can be found here.
After replacing one of 4GB RAM with 16GB one, it throws
1m_ipv4_udp_receive_buffer_errors
frequently, such as
Following the instructions
but no drops
wlp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.13.59.193 netmask 255.255.128.0 broadcast 10.13.127.255
inet6 fe80::def:d34:a2c:da88 prefixlen 64 scopeid 0x20<link>
ether a4:34:d9:e8:9a:bd txqueuelen 1000 (Ethernet)
RX packets 17556713 bytes 20549547923 (20.5 GB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 14008823 bytes 17151970123 (17.1 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
then try to enlarge net.core.rmem_max and net.core.rmem_default. The current values are
~$ sysctl net.core | grep mem
net.core.optmem_max = 20480
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.core.wmem_default = 212992
net.core.wmem_max = 212992
the update it via
~$ sudo sysctl -w net.core.rmem_default=1048576
net.core.rmem_default = 1048576
~$ sudo sysctl -w net.core.rmem_max=2097152
net.core.rmem_max = 2097152
~$ sysctl net.core | grep mem
net.core.optmem_max = 20480
net.core.rmem_default = 1048576
net.core.rmem_max = 2097152
net.core.wmem_default = 212992
net.core.wmem_max = 212992
it seems to work since much fewer warning message of 1m_ipv4_udp_receive_buffer_errors
开机自启动¶
搜索 Startup 便可弹出开机自启动软件界面，
Connect Android Phones¶
If the computer does not recognize the android devices, try to use the original cable. See for other possibilities.