Linux的重要子目录

root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0 
DEVICE=eth0　　#网卡设备名称
HWADDR=00:0C:29:26:96:BD　　#MAC地址
TYPE=Ethernet　　#以太网
UUID=e982e20a-e7ef-4246-8e44-a7c0c474c708　　#Linux系统内部的标识，唯一
ONBOOT=yes　　#开机启动
NM_CONTROLLED=yes　　
#BOOTPROTO=dhclient
BOOTPROTO=static　　#引导协议，一般为static（静态），dhclient（自动获取）
IPADDR=192.168.126.128　　#IP地址

NETMASK=255.255.255.0　　#子网掩码
GATEWAY=192.168.126.2　　#网关
DNS=111.13.148.14

[root@localhost ~]# cat /etc/resolv.conf
; generated by /sbin/dhclient-script
search localdomain
nameserver 192.168.126.2

[root@centos6 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.197.100 centos6.6
[root@centos6 ~]# hostname
centos6.6
[root@centos6 ~]# ping centos6.6
PING centos6.6 (192.168.197.100) 56(84) bytes of data.
64 bytes from centos6.6 (192.168.197.100): icmp_seq=1 ttl=64 time=0.051 ms
64 bytes from centos6.6 (192.168.197.100): icmp_seq=2 ttl=64 time=0.047 ms
64 bytes from centos6.6 (192.168.197.100): icmp_seq=3 ttl=64 time=0.047 ms
^C
-- centos6.6 ping statistics --
3 packets transmitted, 3 received, 0% packet loss, time 2867ms
rtt min/avg/max/mdev = 0.047/0.048/0.051/0.006 ms

[root@localhost ~]# cat /etc/inittab 
# inittab is only used by upstart for the default runlevel.　　#只被用于突然发起的默认运行级别
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
# 
id:3:initdefault:

[root@localhost init.d]# cat /etc/profile
# /etc/profile

# System wide environment and startup programs, for login setup　　#系统全局变量和启动程序
# Functions and aliases go in /etc/bashrc

# It‘s NOT a good idea to change this file unless you know what you　　#除非你知道你要做什么，否则不要更改
# are doing. It‘s much better to create a custom.sh shell script in　　#更好的是去创建脚本在/etc/profile.d，去改变
# /etc/profile.d/ to make custom changes to your environment, as this
# will prevent the need for merging in future updates.

pathmunge () {
    case ":${PATH}:" in
        *:"$1":*)
            ;;
        *)
            if [ "$2" = "after" ] ; then
                PATH=$PATH:$1
            else
                PATH=$1:$PATH
            fi
    esac
}


if [ -x /usr/bin/id ]; then
    if [ -z "$EUID" ]; then
        # ksh workaround
        EUID=`id -u`
        UID=`id -ru`
    fi
    USER="`id -un`"
    LOGNAME=$USER
    MAIL="/var/spool/mail/$USER"
fi

# Path manipulation
if [ "$EUID" = "0" ]; then
    pathmunge /sbin
    pathmunge /usr/sbin
    pathmunge /usr/local/sbin
else
    pathmunge /usr/local/sbin after
    pathmunge /usr/sbin after
    pathmunge /sbin after
fi

HOSTNAME=`/bin/hostname 2>/dev/null`
HISTSIZE=1000
if [ "$HISTCONTROL" = "ignorespace" ] ; then
    export HISTCONTROL=ignoreboth
else
    export HISTCONTROL=ignoredups
fi

export PATH USER LOGNAME MAIL HOSTNAME HISTSIZE HISTCONTROL

# By default, we want umask to get set. This sets it for login shell
# Current threshold for system reserved uid/gids is 200
# You could check uidgid reservation validity in
# /usr/share/doc/setup-*/uidgid file
if [ $UID -gt 199 ] && [ "`id -gn`" = "`id -un`" ]; then
    umask 002
else
    umask 022
fi

for i in /etc/profile.d/*.sh ; do
    if [ -r "$i" ]; then
        if [ "${-#*i}" != "$-" ]; then
            . "$i"
        else
            . "$i" >/dev/null 2>&1
        fi
    fi
done

unset i
unset -f pathmunge
export TMOUT=300
HISTSIZE=50
HISTFILESIZE=50

[root@centos6 ~]# cd /etc/profile.d/
[root@centos6 profile.d]# vi welcome.sh
echo "welcome to mingongge‘s blog"
[root@centos6 profile.d]# chmod +x welcome.sh
[root@centos6 profile.d]# logout
Last login: Thu Dec 22 13:51:55 2016 from 192.168.197.1
welcome to mingongge‘s blog

DESCRIPTION
       Crontab  is  the program used to install, remove or list the tables　　#crontab是程序用来安装，移除或者列出一个表去驱动cron进程。
       used to drive the cron(8) daemon.  Each user  can  have  their  own
       crontab,  and  though these are files in /var/spool/ , they are not　　#这些定时文件到在/var/spool/cron下
       intended to be edited directly. For SELinux in mls mode can be even
       more crontabs - for each range. For more see selinux(8).

       The  cron  jobs could be allow or disallow for different users. For
       classical crontab there exists cron.allow and cron.deny files.   If
       cron.allow file exists, then you must be listed therein in order to
       be allowed to use this command.  If the cron.allow  file  does  not
       exist  but  the  cron.deny  file  does  exist, then you must not be
       listed in the cron.deny file in order to use this command.  If nei-
       ther  of these files exists, only the super user will be allowed to
       use this command.  The second option is using  PAM  authentication,
       where  you  set  up  users, which could or couldn’t use crontab and
       also system cron jobs from /etc/cron.d/.

       The temporary directory could be set in  enviroment  variables.  If
       it’s not set by user than /tmp is used.