Users who do not exist in /etc/sudoers will not have permission to run command sudo ..., add the following line to this file:

<username> ALL=(ALL) ALL

Now the user <username> will have the root privileges.

Input password every time when you run sudo ... is really annoying, put the following line into /etc/sudoers/:

Defaults:<username> !authenticate

Now the user <username> will not need to input password any more when running sudo ....

touch /etc/network.d/home  # the file name can be whatever you like
vi /etc/network.d/home

then input the following contents:

CONNECTION="wireless"
ESSID="<my network>"  # replace it with the real network ESSID
INTERFACE="wlan0"
SCAN="yes"
IP="dhcp"
TIMEOUT="10"
SECURITY="wpa"
KEY="<passphrase>"    # replace it with your real passphrase

then save this file, run the following command:

netcfg home

Now your network will be up.

Other useful commands:

ip link set wlan0 up/down # take up/down the wireless network
ip addr show wlan0        # show state of the wireless network
iwlist wlan0 scan         # scan available wireless points
iw dev wlan0 scan         # same as above

Command wifi-menu is also very useful in package netcfg.

pacman -Qo /path/to/file

When updating archlinux through pacman with pacman -Syu, below error occurs:

error: dropbox: missing required signature :: File /var/cache/pacman/pkg/dropbox-2.0.8-1-x86_64.pkg.tar.xz is corrupted (invalid or corrupted package (PGP signature)). Do you want to delete it? [Y/n] y error: failed to commit transaction (invalid or corrupted package) Errors occurred, no packages were upgraded.

Solution: modify /etc/pacman.conf, change the value of global SigLevel into Optional TrustAll.

#SigLevel = Required DatabaseOptional
SigLevel  = Optional TrustAll

netstat -anput

-a) established和listen都显示

-n) 显示数字，如127.0.0.1:80，而不是localhost:http

-p) 显示占用此端口的PID和程序名称

-u/-t) 显示TCP和UDP，查端口占用基本只有TCP/UDP是有用的，其它那些STREAM的根本不知道是神马类型。。

如果有装lsof的话，也可以用以下命令查看8080的端口占用：

lsof -i :8080

ldd [-v] <path/to/binary>

or

readelf

Emacs选择的默认快捷键是Ctrl + Space，和fcitx的激活快捷键Ctrl + Space冲突。

解决方法 ：修改 ~/.config/fcitx/config ：

TriggerKey=CTRL_RSHIFT    # default value is CTRL_SPACE
IMSwitchHotkey=ALT_SUPER  # default value is CTRL_SHIFT

将TriggerKey由默认的Ctrl + Space改为Ctrl + Right Shift，但是由于另外一个选项也是Ctrl + Shift，有冲突，所以把冲突的IMSwitchHotkey给改掉。

然后，重启fcitx，这样fcitx和emacs的快捷键冲突就解决了。

要在emacs中输入中文，还需要设置LC_CTYPE为zh_CN.UTF-8，不然依旧无法输入。比较好的解决方法：

sudo mv /usr/bin/emacs /usr/bin/emacs.origin
sudo touch /usr/bin/emacs
sudo chmod 755 /usr/bin/emacs

然后，在 /usr/bin/emacs 中输入以下内容：

#!/bin/zsh
LC_CTYPE=zh_CN.UTF-8
/usr/bin/emacs.origin "$@"

再运行emacs就可以输入中文。

有些电影本身就是双语的，这时候只需要切换一下音轨就可以了：

mplayer ... -aid 0/1 (for more than one language)

至于音轨的信息在mplayer播放的时候，会在命令行输出，所以只需要先试着播放一下，然后看命令行的音轨信息，再按照上面加上参数就可以了。

不太清楚mplayer默认使用的是什么编码，但肯定有些字幕采用的编码和mplayer默认使用的编码不同，这就导致播放的时候会乱码，但因为大家都是天朝人，所以还是可以大致猜到字幕的编码的，一般情况加上下面的参数就OK了：

mplayer ... -subcp cp936

如果加上这个参数后，还是显示有乱码，那就再试试其它编码，gb2312神马的，总有一个是可以的。