ifup 和 ifdown 相关脚本

 

1 概述

 

网卡可以通过 ifconfig 进行临时配置，也可以将配置内容写入/etc/sysconfig/network-scripts/ifcfg-ethx进行永久配置，然后执行 ifup/ifdown 会自动加载配置，进行网卡的启动和停止。这里主要描述 ifup/ifdown 调用的过程。

 

 

 

 

 

2 ifup 和 ifdown 流程

 

(1) 网卡根据网络配置的启动，需要根据四个主要脚本

(a) 启动和停止脚本：/sbin/ifup 和 /sbin/ifdown

(b) 具体启动和停止脚本：/etc/sysconfig/network-scripts/ifup-eth 和 /etc/sysconfig/network-scripts/ifdown-eth

(c) 执行函数：/etc/sysconfig/network-scripts/network-functions

 

 

(2) 执行顺序

ifup/ifdown --->ifup-eth/ifown-eth--->network-function

 

 

(3) 启动和停止命令

ifup ethx
ifdown ethx

 

 

 

 

3 注意

 

3.1 DHCP模式执行过程

 

dhcclient 是dhcp客户端程序，选择dhcp获取ip地址的需要用到。dhclient 启动的时候会先找dhclient配置文件，寻找顺序为：先找该网口配置文件 /etc/dhcp/dhclient-ethx.conf，若找不到则找/etc/dhclient-ethx.conf，若找不到则不使用配置文件启动dhclient。

 

(1) 查找对应网卡 dhclient 配置文件

generate_config_file_name ()
{
    local ver=$1
    if [ -s /etc/dhcp/dhclient$ver-${DEVICE}.conf ]; then
        DHCLIENTCONF="-cf /etc/dhcp/dhclient$ver-${DEVICE}.conf";
    elif [ -s /etc/dhclient$ver-${DEVICE}.conf ]; then
        DHCLIENTCONF="-cf /etc/dhclient$ver-${DEVICE}.conf";
    else
        DHCLIENTCONF='';
    fi
}

 

 

 

(2) 启动dhclient

 

if [ -n "${DYNCONFIG}" ] && [ -x /sbin/dhclient ]; then
    if is_true "${PERSISTENT_DHCLIENT}"; then
        ONESHOT="";
    else
        ONESHOT="-1";
    fi;
    
    # 查找配置文件，然后生成配置文件名
    generate_config_file_name
    generate_lease_file_name

    # Initialize the dhclient args and obtain the hostname options if needed:
    # dhclient 参数
    DHCLIENTARGS="${DHCLIENTARGS} ${ONESHOT} -q ${DHCLIENTCONF} -lf ${LEASEFILE} 
                  -pf /var/run/dhclient-${DEVICE}.pid"
    set_hostname_options DHCLIENTARGS

    echo
    echo -n $"Determining IP information for ${DEVICE}..."
    if ! is_true "${PERSISTENT_DHCLIENT}" && check_link_down ${DEVICE}; then
        echo $" failed; no link present.  Check cable?"
        exit 1
    fi

    ethtool_set

    # 启动dhclient
    if /sbin/dhclient ${DHCLIENTARGS} ${DEVICE} ; then
        echo $" done."
        dhcpipv4="good"
    else
        echo $" failed."
        if is_true "${IPV4_FAILURE_FATAL}"; then
            exit 1
        fi
        if is_false "$IPV6INIT" || ! is_true "$DHCPV6C"; then
            exit 1
        fi
        net_log "Unable to obtain IPv4 DHCP address ${DEVICE}." warning
    fi
    # end dynamic device configuration
else