《鸟哥的Linux私房菜》学习笔记（2）——Bash特性
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时间：2015年06月20日
bash及其特性：
离用户最近的程序是shell,shell 是外壳的意思,本身也是一种可执行程序。广义上的shell包含两类GUI和CLI。
GUI:Gnome,KDE,Xface
CLI:sh,csh,ksh,bash,tcsh,zsh
当有多个用户登陆的时候，会有多个进程，进程之间彼此互不相干，因为对于每个进程来说，它只认为当前主机上只有自己和内核存在。但是只有一个shell程序。linux允许一个用户账号登陆多次 。
进程是程序的副本，进程是程序执行的实例，是有生命周期的，由内核进行管理。
用户工作环境，多个用户尽管使用的都是shell程序，但是各个用户的工作环境设定却可以各不相同，只不过默认情况下除了管理员，都是一样的。
shell，子shell。可以在一个shell中在启动一个子shell。下面的通过pstree命令可以看出该关系，如果退出到上一层bash，可以用exit命令。退到最上一层时候，会退出登陆。
[hao@hao ~]$ bash [hao@hao ~]$ pstree init-+-NetworkManager-+-dhclient | `-{NetworkManager} |-abrtd |-acpid |-atd |-auditd---{auditd} |-automount---4*[{automount}] |-bonobo-activati---{bonobo-activat} |-certmonger |-clock-applet |-console-kit-dae---63*[{console-kit-da}] |-crond |-cupsd |-2*[dbus-daemon---{dbus-daemon}] |-2*[dbus-launch] |-devkit-power-da |-gconf-im-settin |-gconfd-2 |-gdm-binary-+-gdm-simple-slav-+-Xorg | | |-gdm-session-wor-+-gnome-session-+-abrt-applet | | | | |-bluetooth-apple | | | | |-evolution-alarm | | | | |-gdu-notificatio | | | | |-gnome-panel | | | | |-gnome-power-man | | | | |-gnome-volume-co | | | | |-gpk-update-icon | | | | |-metacity | | | | |-nautilus | | | | |-nm-applet | | | | |-polkit-gnome-au | | | | |-python | | | | |-restorecond | | | | `-{gnome-session} | | | `-{gdm-session-wo} | | `-{gdm-simple-sla} | `-{gdm-binary} |-gdm-user-switch |-gnome-keyring-d---2*[{gnome-keyring-}] |-gnome-screensav |-gnome-settings----{gnome-settings} |-gnote |-gvfs-afc-volume---{gvfs-afc-volum} |-gvfs-gdu-volume |-gvfs-gphoto2-vo |-gvfsd |-gvfsd-burn |-gvfsd-computer |-gvfsd-metadata |-gvfsd-trash |-hald-+-hald-runner-+-hald-addon-acpi | | `-hald-addon-inpu | `-{hald} |-ibus-x11 |-im-settings-dae-+-ibus-daemon-+-ibus-engine-pin | | |-ibus-gconf | | |-python | | `-{ibus-daemon} | `-{im-settings-da} |-login---bash---su---bash |-master-+-pickup | `-qmgr |-4*[mingetty] |-modem-manager |-notification-ar |-polkitd |-pulseaudio-+-gconf-helper | `-2*[{pulseaudio}] |-rpc.statd |-rpcbind |-rsyslogd---3*[{rsyslogd}] |-rtkit-daemon---2*[{rtkit-daemon}] |-seahorse-daemon |-sshd---sshd---sshd---bash---bash---pstree |-trashapplet |-udevd---2*[udevd] |-udisks-daemon-+-udisks-daemon | `-{udisks-daemon} |-wnck-applet `-wpa_supplicant [hao@hao ~]$ bash [hao@hao ~]$ pstree init-+-NetworkManager-+-dhclient | `-{NetworkManager} |-abrtd |-acpid |-atd |-auditd---{auditd} |-automount---4*[{automount}] |-bonobo-activati---{bonobo-activat} |-certmonger |-clock-applet |-console-kit-dae---63*[{console-kit-da}] |-crond |-cupsd |-2*[dbus-daemon---{dbus-daemon}] |-2*[dbus-launch] |-devkit-power-da |-gconf-im-settin |-gconfd-2 |-gdm-binary-+-gdm-simple-slav-+-Xorg | | |-gdm-session-wor-+-gnome-session-+-abrt-applet | | | | |-bluetooth-apple | | | | |-evolution-alarm | | | | |-gdu-notificatio | | | | |-gnome-panel | | | | |-gnome-power-man | | | | |-gnome-volume-co | | | | |-gpk-update-icon | | | | |-metacity | | | | |-nautilus | | | | |-nm-applet | | | | |-polkit-gnome-au | | | | |-python | | | | |-restorecond | | | | `-{gnome-session} | | | `-{gdm-session-wo} | | `-{gdm-simple-sla} | `-{gdm-binary} |-gdm-user-switch |-gnome-keyring-d---2*[{gnome-keyring-}] |-gnome-screensav |-gnome-settings----{gnome-settings} |-gnote |-gvfs-afc-volume---{gvfs-afc-volum} |-gvfs-gdu-volume |-gvfs-gphoto2-vo |-gvfsd |-gvfsd-burn |-gvfsd-computer |-gvfsd-metadata |-gvfsd-trash |-hald-+-hald-runner-+-hald-addon-acpi | | `-hald-addon-inpu | `-{hald} |-ibus-x11 |-im-settings-dae-+-ibus-daemon-+-ibus-engine-pin | | |-ibus-gconf | | |-python | | `-{ibus-daemon} | `-{im-settings-da} |-login---bash---su---bash |-master-+-pickup | `-qmgr |-4*[mingetty] |-modem-manager |-notification-ar |-polkitd |-pulseaudio-+-gconf-helper | `-2*[{pulseaudio}] |-rpc.statd |-rpcbind |-rsyslogd---3*[{rsyslogd}] |-rtkit-daemon---2*[{rtkit-daemon}] |-seahorse-daemon |-sshd---sshd---sshd---bash---bash---bash---pstree |-trashapplet |-udevd---2*[udevd] |-udisks-daemon-+-udisks-daemon | `-{udisks-daemon} |-wnck-applet `-wpa_supplicant
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