一：设置环境变量的三种方法_xuqryu

1.1 临时设置
export PATH=/home/yan/share/usr/local/arm/3.4.1/bin:$PATH
1.2 当前用户的全局设置
打开~/.bashrc，添加行：

export PATH=/home/yan/share/usr/local/arm/3.4.1/bin:$PATH
使生效：

source .bashrc
1.3 所有用户的全局设置
$ vim /etc/profile
在里面加入：

export PATH=/home/yan/share/usr/local/arm/3.4.1/bin:$PATH
使生效

source profile
二： 测试当前的环境变量
echo $PATH
或
env
用户登录后加载profile和bashrc的流程如下:

1. /etc/profile
   ->/etc/profile.d/*.sh

2. $HOME/.bas{h}_{p}rofile->$HOME/.bashrc
   ->/etc/bashrc
   说明:
   bash首先执行/etc/profile脚本,/etc/profile脚本先依次执行/etc/profile.d/*.sh
   随后bash会执行用户主目录下的.bash_profile脚本,.bash_profile脚本会执行用户主目录下的.bashrc脚本,
   而.bashrc脚本会执行/etc/bashrc脚本。
   至此,所有的环境变量和初始化设定都已经加载完成.
   bash随后调用terminfo和inputrc，完成终端属性和键盘映射的设定.

其中PATH这个变量特殊说明一下:

如果是超级用户登录,在没有执行/etc/profile之前,PATH已经设定了下面的路径:
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
如果是普通用户,PATH在/etc/profile执行之前设定了以下的路径:
/usr/local/bin:/bin:/usr/bin
这里要注意的是:在用户切换并加载变量,例如su -,这时，如果用户自己切换自己,比如root用户再用su - root切换的话,加载的PATH和上面的不一样.
准确的说，是不总是一样.所以，在/etc/profile脚本中，做了如下的配置:

if [ id -u = 0 ]; then
pathmunge /sbin
pathmunge /usr/sbin
pathmunge /usr/local/sbin
fi
如果是超级用户登录,在/etc/profile.d/krb5.sh脚本中,在PATH变量搜索路径的最前面增加/usr/kerberos/sbin:/usr/kerberos/bin
如果是普通用户登录,在/etc/profile.d/krb5.sh脚本中,在PATH变量搜索路径的最前面增加/usr/kerberos/bin

在/etc/profile脚本中,会在PATH变量的最后增加/usr/X11R6/bin目录
在HOME/.bashprofile中,会在PATH变量的最后增加HOME/.bashprofile中,会在PATH变量的最后增加HOME/bin目录

以root用户为例,最终的PATH会是这样(没有其它自定义的基础上)

/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin
以alice用户(普通用户)为例

/usr/kerberos/bin:/usr/bin:/bin:/usr/X11R6/bin:/home/alice/bin
三：脚本解析
###############################################
#strace -o su -e trace=open su - alice
#grep ^open /etc/su|grep -v null|grep “= 3”|nl
###############################################
3.1 打开的文件如下:
1 open("/etc/ld.so.cache", O_RDONLY) = 3
2 open("/lib/libcrypt.so.1", O_RDONLY) = 3
3 open("/lib/tls/libc.so.6", O_RDONLY) = 3
4 open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
5 open("/etc/nsswitch.conf", O_RDONLY) = 3
6 open("/etc/ld.so.cache", O_RDONLY) = 3
7 open("/lib/libnss_files.so.2", O_RDONLY) = 3
8 open("/etc/passwd", O_RDONLY) = 3
9 open("/etc/shadow", O_RDONLY) = 3
10 open("/etc/group", O_RDONLY) = 3
11 open("/etc/ld.so.cache", O_RDONLY) = 3
12 open("/lib/libtermcap.so.2", O_RDONLY) = 3
13 open("/lib/libdl.so.2", O_RDONLY) = 3
14 open("/lib/tls/libc.so.6", O_RDONLY) = 3
15 open("/dev/tty", O_RDWR|O_NONBLOCK|O_LARGEFILE) = 3
16 open("/etc/mtab", O_RDONLY) = 3
17 open("/proc/meminfo", O_RDONLY) = 3
18 open("/etc/nsswitch.conf", O_RDONLY) = 3
19 open("/etc/ld.so.cache", O_RDONLY) = 3
20 open("/lib/libnss_files.so.2", O_RDONLY) = 3
21 open("/etc/passwd", O_RDONLY) = 3
22 open("/etc/profile", O_RDONLY|O_LARGEFILE) = 3
23 open("/etc/profile.d/", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 3
24 open("/etc/profile.d/colorls.sh", O_RDONLY|O_LARGEFILE) = 3
25 open(".", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 3
26 open("/etc/profile.d/glib2.sh", O_RDONLY|O_LARGEFILE) = 3
27 open("/etc/profile.d/gnome-ssh-askpass.sh", O_RDONLY|O_LARGEFILE) = 3
28 open("/etc/profile.d/krb5.sh", O_RDONLY|O_LARGEFILE) = 3
29 open("/etc/profile.d/lang.sh", O_RDONLY|O_LARGEFILE) = 3
30 open("/etc/sysconfig/i18n", O_RDONLY|O_LARGEFILE) = 3
31 open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
32 open("/usr/lib/gconv/gconv-modules.cache", O_RDONLY) = 3
33 open("/etc/profile.d/less.sh", O_RDONLY|O_LARGEFILE) = 3
34 open("/etc/profile.d/qt.sh", O_RDONLY|O_LARGEFILE) = 3
35 open("/etc/profile.d/vim.sh", O_RDONLY|O_LARGEFILE) = 3
36 open("/etc/profile.d/which-2.sh", O_RDONLY|O_LARGEFILE) = 3
37 open("/ceno/prod t/imeg/etc/profile", O_RDONLY|O_LARGEFILE) = 3
38 open("/home/alice/.bash_profile", O_RDONLY|O_LARGEFILE) = 3
39 open("/home/alice/.bashrc", O_RDONLY|O_LARGEFILE) = 3
40 open("/etc/bashrc", O_RDONLY|O_LARGEFILE) = 3
41 open("/home/alice/.bash_history", O_RDONLY|O_LARGEFILE) = 3
42 open("/home/alice/.bash_history", O_RDONLY|O_LARGEFILE) = 3
43 open("/etc/termcap", O_RDONLY) = 3
44 open("/etc/inputrc", O_RDONLY|O_LARGEFILE) = 3
45 open(".", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 3
46 open("/home/alice/.bash_logout", O_RDONLY|O_LARGEFILE) = 3
47 open("/home/alice/.bash_history", O_WRONLY|O_APPEND|O_LARGEFILE) = 3
48 open("/home/alice/.bash_history", O_RDONLY|O_LARGEFILE) = 3
3.2 脚本解析说明
3.2.1 第一部分
从1-21行基本是打开动态链接库文件和身份验证的文件.

3.2.2 第二部分
第22行是打开/etc/profile文件,如下:

/etc/profile

System wide environment and startup programs, for login setup

Functions and aliases go in /etc/bashrc

#定义pathmunge函数
#echo $PATH | /bin/egrep -q "(^|:)$1($|:)"是过滤KaTeX parse error: Expected 'EOF', got '#' at position 32: …rep到批配项,返回真但取反 #̲也就是不增加执行目录到PATH中,选项-q禁止所有的输出到标准输出，不管匹配行。如果选中输入行，以 0 状态退出
#这里由 | (竖线)或者换行符隔开的多个正则表达式会匹配与任何一个正则表达式所匹配的字符串
#一个正则表达式可以被包括在“()”（括弧）中进行分组
pathmunge () {
if ! echo $PATH | /bin/egrep -q “(^|:)$1($|:)” ; then
if [ "$2"="after"];thenPATH=$PATH:$1
else
PATH=$1:$PATH
fi
fi
}
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