The Internet Systems Consortium DHCP Client, dhclient, provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol, BOOTP protocol, or if these protocols fail, by statically assigning an address.
The DHCP protocol allows a host to contact a central server which maintains a list of IP addresses which may be assigned on one or more subnets. A DHCP client may request an address from this pool, and then use it on a temporary basis for communication on network. The DHCP protocol also provides a mechanism whereby a client can learn important details about the network to which it is attached, such as the location of a default router, the location of a name server, etc.
On startup, dhclient reads the file dhclient.conf for configuration instructions. It then gets a list of all the network interfaces that are configured in the current system. For each interface, it attempts to configure the interface using the DHCP protocol.
To keep track of leases across system reboots and server restarts, dhclient keeps a list of leases it was assigned in the dhclient.leases file. On startup, after reading the dhclient.conf file, dhclient reads the dhclient.leases file to refresh its memory about what leases it was assigned.
When a new lease is acquired, it is appended to the end of the dhclient.leases file. To prevent the file from becoming arbitrarily large, from time to time dhclient creates a new dhclient.leases file from its in-core lease database. The old version of the dhclient.leases file is retained under the name dhclient.leases~ until the next time dhclient rewrites the database.
Old leases are kept around in case the DHCP server is unavailable when dhclient is first invoked (generally during the initial system boot process). In that event, old leases from the dhclient.leases file which have not yet expired are tested, and if they are determined to be valid, they are used until either they expire or the DHCP server becomes available.
A mobile host which may sometimes need to access a network on which no DHCP server exists may be preloaded with a lease for a fixed address on that network. When all attempts to contact a DHCP server have failed, dhclient will try to validate the static lease, and if it succeeds, will use that lease until it is restarted.
A mobile host may also travel to some networks on which DHCP is not available but BOOTP is. In that case, it may be advantageous to arrange with the network administrator for an entry on the BOOTP database, so that the host can boot quickly on that network rather than cycling through the list of old leases.
Use the DHCPv4 protocol to obtain an IPv4 address and configuration parameters (default).
-6
Use the DHCPv6 protocol to obtain whatever IPv6 addresses are available along with configuration parameters. The functionality of DHCPv6 mode may be modified with the -S, -T, and -N options.
-S
Perform an information-only request over DHCPv6 to get stateless configuration parameters. It is not recommended to combine this option with the -N, -P, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-N
Perform a normal (IA_NA) address query over DHCPv6. It is not recommended to combine this option with the -P, -S, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-T
Perform a temporary (IA_TA) address query over DHCPv6 (disables normal address query). It is not recommended to combine this option with the -N, -P, or -S options or share lease files between different modes of operation. Only valid with the -6 option.
-P
Enable IPv6 prefix delegation (disables normal address query). It is not recommended to combine this option with the -N, -S, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-p
The UDP port number the DHCP client should listen and transmit. If unspecified, dhclient uses the default port 68. This option is mostly useful for debugging purposes. If a different port is specified for the client to listen and transmit on, the client will also use a different destination port: one less than the specified port.
-d
Force dhclient to run as a foregroundprocess. This is useful when running the client under a debugger, or when running it out of inittab on System V systems.
-eVAR=value
Define additional environment variables for the environment where dhclient-script executes. You may specify multiple -e options on the command line. For example: -e IF_METRIC=1
-q
Suppress all terminal and log output except error messages.
-1
Try once to get a lease. One failure, exit with code 2.
-r
Tell dhclient to release the current lease it has from the server. This is not required by the DHCP protocol, but some ISPs require their clients to notify the server if they wish to release an assigned IP address.
-lf
Path to the lease database file. If unspecified, the default /var/lib/dhclient/dhclient.leases is used.
-pf
Path to the process ID file. If unspecified, the default /var/run/dhclient.pid is used.
-cf
Path to the client configuration file. If unspecified, the default /etc/dhcp/dhclient.conf is used.
-sf
Path to the network configuration script invoked by dhclient when it gets a lease. If unspecified, the default /sbin/dhclient-script is used.
-s
Specify the server IP address or fully qualified domain name to transmit DHCP protocol messages. Normally, dhclient transmits these messages to 255.255.255.255 (the IP limited broadcast address). Overriding this is mostly useful for debugging purposes.
-g
Only for debugging. Set the giaddr field of all packets the client sends to the IP address specified. This should not be expected to work in any consistent or useful way.
-n
Do not configure any interfaces. Most useful combined with the -w option.
-nc
Do not drop capabilities.
Normally, if dhclient was compiled with libcap-ng support, dhclient drops most capabilities immediately upon startup. While more secure, this greatly restricts the additional actions that hooks in dhclient-script can take. (For example, any daemons that dhclient-script starts or restarts will inherit the restricted capabilities as well, which may interfere with their correct operation.) Thus, the -nc option can be used to prevent dhclient from dropping capabilities.
The -nc option is ignored if dhclient was not compiled with libcap-ng support.
-nw
Become a daemon process immediately (nowait) rather than waiting until an IP address is acquired.
-w
Keep running even if no network interfaces are found. The omshell program can be used to notify the client when a network interface is added or removed so it can attempt to configure an IP address on that interface.
-B
Set the BOOTP broadcast flag in request packets so servers will always broadcast replies.
-I
Specify the dhcp-client-identifier option to send to the DHCP server.
-H
Specify the host-name option to send to the DHCP server. The host-name string only contains the client's hostname prefix, to which the server will append the ddns-domainname or domain-name options, if any, to derive the fully qualified domain name of the client. The -H option cannot be used with the -F option.
-F
Specify the fqdn.fqdn option to send to the DHCP server. This option cannot be used with the -H option. The fqdn.fqdn option must specify the complete domain name of the client host, which the server may use for dynamic DNS updates.
-V
Specify the vendor-class-identifier option to send to the DHCP server.
-R [,...]
Specify the list of options the client is to request from the server. The option list must be a single string consisting of option names separated by at least one command and optional space characters. The default option list is:
The -R option does not append options to the default request, it overrides the default request list. Keep this in mind if you want to request an additional option besides the default request list. You have to specify all option names for the -R parameter.
-timeout
Specify the time after which dhclient will decide that no DHCP servers can be contacted when no responses have been received.
-v
Enable verbose log messages.
If the client is killed by a signal (for example at shutdown or reboot), it will not execute the dhclient-script at exit. However, if you shut the client down gracefully with -r or -x it will execute dhclient-script at shutdown with the specific reason for calling the script set in the environment table.
Omapi
The DHCP client provides some ability to control it while it is running, without stopping it. This capability is provided using OMAPI, an API for manipulating remote objects. OMAPI clients connect to the client using TCP/IP, authenticate, and can then examine the client's current status and make changes to it.
Rather than implementing the underlying OMAPI protocol directly, user programs should use the dhcpctl API or OMAPI itself. Dhcpctl is a wrapper that handles some of the housekeeping chores that OMAPI does not do automatically. Most things you'd want to do with the client can be done directly using the omshell command, rather than having to write a special program.
The control object
The control object allows you to shut the client down, releasing all leases that it holds and deleting any DNS records it may have added. It also allows you to pause the client - this unconfigures any interfaces the client is using. You can then restart it, which causes it to reconfigure those interfaces. You would normally pause the client before going into hibernation or sleep on a laptop computer. You would then resume it after the power comes back. This allows PC cards to be shut down while the computer is hibernating or sleeping, and then reinitialized to their previous state once the computer comes out of hibernation or sleep.
The control object has one attribute - the state attribute. To shut the client down, set its state attribute to 2. It will automatically do a DHCPRELEASE. To pause it, set its state attribute to 3. To resume it, set its state attribute to 4.
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dhclient 例子
dhclient eth0
更新主以太網設備的動態分配的IP地址。
dhclient eth0
Renews the dynamically-assigned IP address of a primary Ethernet device.
dhclient (提供了一種用于配置一個或使用動態主機配置協議多個網絡接口)
互聯網系統聯盟DHCP客戶端，dhclient的，提供了一種用于配置一個或使用動態主機配置協議多個網絡接口，一個裝置BOOTP協議，或者如果這些協議失敗，由靜態分配一個地址。
The Internet Systems Consortium DHCP Client, dhclient, provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol, BOOTP protocol, or if these protocols fail, by statically assigning an address.
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1 dhclient 運行系統環境
2 dhclient 描述
3 dhclient 語法
4 dhclient 例子
dhclient 運行系統環境
Unix&Linux
dhclient 描述
DHCP協議允許主機與維護可在一個或多個子網中分配的IP地址列表的中央服務器聯系。DHCP客戶端可以從該池中請求一個地址，然后將其臨時用于網絡上的通信。DHCP協議還提供了一種機制，客戶端可以通過該機制來了解有關其所連接的網絡的重要信息，例如默認路由器的位置，名稱服務器的位置等。
啟動時，dhclient讀取文件dhclient.conf以獲取配置說明。然后，它將獲取當前系統中配置的所有網絡接口的列表。對于每個接口，它嘗試使用DHCP協議配置接口。
為了跟蹤系統重新啟動和服務器重新啟動之間的租約，dhclient會在dhclient.leases文件中保留分配給它的租約列表。啟動時，讀取dhclient.conf文件后，dhclient讀取dhclient.leases文件以刷新其內存，了解分配的租約。
當獲取新的租約時，它將被附加到dhclient.leases文件的末尾。為了防止文件任意增大，dhclient會不時從其核心租用數據庫中創建一個新的dhclient.leases文件。dhclient.leases文件的舊版本將保留為dhclient.leases?名稱，直到下次dhclient重寫數據庫為止。
萬一第一次調用dhclient時（通常在初始系統引導過程中），DHCP服務器不可用，則保留舊租約。在這種情況下，將測試來自dhclient.leases文件的尚未到期的舊租約，如果確定它們是有效的，則將使用這些租約，直到它們過期或DHCP服務器可用為止。
有時可能需要訪問不存在DHCP服務器的網絡的移動主機可能會預先租用該網絡上固定地址的租約。當所有嘗試聯系DHCP服務器的嘗試均失敗時，dhclient將嘗試驗證靜態租約，如果成功，將使用該租約直到重新啟動。
移動主機也可能會訪問某些DHCP不可用但BOOTP可用的網絡。在這種情況下，與網絡管理員安排BOOTP數據庫中的條目可能是有利的，以便主機可以在該網絡上快速啟動，而不是循環瀏覽舊租賃列表。
The DHCP protocol allows a host to contact a central server which maintains a list of IP addresses which may be assigned on one or more subnets. A DHCP client may request an address from this pool, and then use it on a temporary basis for communication on network. The DHCP protocol also provides a mechanism whereby a client can learn important details about the network to which it is attached, such as the location of a default router, the location of a name server, etc.
On startup, dhclient reads the file dhclient.conf for configuration instructions. It then gets a list of all the network interfaces that are configured in the current system. For each interface, it attempts to configure the interface using the DHCP protocol.
To keep track of leases across system reboots and server restarts, dhclient keeps a list of leases it was assigned in the dhclient.leases file. On startup, after reading the dhclient.conf file, dhclient reads the dhclient.leases file to refresh its memory about what leases it was assigned.
When a new lease is acquired, it is appended to the end of the dhclient.leases file. To prevent the file from becoming arbitrarily large, from time to time dhclient creates a new dhclient.leases file from its in-core lease database. The old version of the dhclient.leases file is retained under the name dhclient.leases~ until the next time dhclient rewrites the database.
Old leases are kept around in case the DHCP server is unavailable when dhclient is first invoked (generally during the initial system boot process). In that event, old leases from the dhclient.leases file which have not yet expired are tested, and if they are determined to be valid, they are used until either they expire or the DHCP server becomes available.
A mobile host which may sometimes need to access a network on which no DHCP server exists may be preloaded with a lease for a fixed address on that network. When all attempts to contact a DHCP server have failed, dhclient will try to validate the static lease, and if it succeeds, will use that lease until it is restarted.
A mobile host may also travel to some networks on which DHCP is not available but BOOTP is. In that case, it may be advantageous to arrange with the network administrator for an entry on the BOOTP database, so that the host can boot quickly on that network rather than cycling through the list of old leases.
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dhclient 語法
dhclient [ -4 | -6 ] [ -S ] [ -N [ -N... ] ] [ -T [ -T... ] ] [ -P [ -P... ] ] [ -p port ] [ -d ] [ -e VAR=value ] [ -q ] [ -1 ] [ -r | -x ] [ -lf lease-file ] [ -pf pid-file ] [ -cf config-file ] [ -sf script-file ] [ -s server ] [ -g relay ] [ -n ] [ -nc ] [ -nw ] [ -w ] [ -B ] [ -I dhcp-client-identifier ] [ -H host-name ] [ -F fqdn.fqdn ] [ -V vendor-class-identifier ] [ -R request-option-list ] [ -timeout timeout ] [ -v ] [ --version ] [ if0 [ ...ifN ] ]選件
-4
使用DHCPv4協議獲取IPv4地址和配置參數（默認）。
-6
使用DHCPv6協議獲取可用的任何IPv6地址以及配置參數。可以使用-S，-T和-N選項修改DHCPv6模式的功能。
-S
通過DHCPv6執行僅信息請求，以獲取無狀態配置參數。不建議將此選項與-N，-P或-T選項結合使用，或在不同的操作模式之間共享租用文件。僅在-6選項下有效。
-N
通過DHCPv6執行常規（IA_NA）地址查詢。不建議將此選項與-P，-S或-T選項結合使用，或在不同的操作模式之間共享租用文件。僅在-6選項下有效。
-T
通過DHCPv6執行臨時（IA_TA）地址查詢（禁用普通地址查詢）。不建議將此選項與-N，-P或-S選項結合使用，或在不同的操作模式之間共享租用文件。僅在-6選項下有效。
-P
啟用IPv6前綴委托（禁用普通地址查詢）。不建議將此選項與-N，-S或-T選項結合使用，或在不同的操作模式之間共享租用文件。僅在-6選項下有效。
-p
DHCP客戶端應偵聽和傳輸的UDP端口號。如果未指定，則dhclient使用默認端口68。此選項主要用于調試目的。如果為客戶端指定了其他端口以進行偵聽和傳輸，則客戶端還將使用其他目標端口：比指定端口少一個。
-d
強制dhclient作為前臺 進程運行。在調試器下運行客戶端或在System V系統上的inittab中運行客戶端時，此功能很有用。
-e VAR =value
定義其他環境變量的環境，這里的dhclient腳本執行。您可以在命令行上指定多個-e選項。例如：-e IF_METRIC = 1
-q
禁止顯示所有終端和日志輸出（錯誤消息除外）。
-1
嘗試一次以獲得租約。一次失敗，退出并輸入代碼2。
-r
告訴dhclient從服務器釋放其當前的租約。DHCP協議不需要這樣做，但是某些ISP要求其客戶端如果希望釋放分配的IP地址，則通知服務器。
-lf
租約數據庫文件的路徑。如果未指定，則使用默認的/var/lib/dhclient/dhclient.leases。
-pf
進程標識文件的路徑。如果未指定，則使用默認的/var/run/dhclient.pid。
-cf
客戶端配置文件的路徑。如果未指定，則使用默認的/etc/dhcp/dhclient.conf。
-sf
dhclient租用時調用的網絡配置腳本的路徑。如果未指定，則使用默認的/ sbin / dhclient-script。
-s
指定服務器IP地址或標準域名以傳輸DHCP協議消息。通常，dhclient將這些消息傳輸到255.255.255.255（IP受限廣播地址）。覆蓋它對于調試目的最有用。
-g
僅用于調試。將客戶端發送的所有數據包的giaddr字段設置為指定的IP地址。不應期望它以任何一致或有用的方式工作。
-n
不要配置任何接口。與-w選項結合使用時最有用。
-nc
不要放棄功能。
通常，如果dhclient在libcap-ng支持下進行編譯，則dhclient在啟動時會立即放棄大多數功能。雖然更安全，但這極大地限制了dhclient-script中的鉤子可以執行的其他操作。（例如，dhclient-script啟動或重新啟動的所有守護程序也會繼承受限的功能，這可能會干擾其正確的操作。）因此，-nc選項可用于防止dhclient丟棄功能。
該-nc如果dhclient的未經編譯選項被忽略的libcap-ng的支持。
-nw
立即（不等待）成為守護進程，而不是等到獲取IP地址后再進行。
-w
即使未找到網絡接口，也要繼續運行。該omshell程序可以用來通知客戶端時，網絡接口被添加或移除，因此它可以嘗試在接口上配置的IP地址。
-B
在請求數據包中設置BOOTP廣播標志，以便服務器將始終廣播答復。
-I
指定dhcp-client-identifier選項以發送到DHCP服務器。
-H
指定主機名選項以發送到DHCP服務器。該主機名字符串僅包含客戶端的主機名前綴，到服務器將追加DDNS，域名或域名的選擇，如果有的話，以獲得客戶端的完全合格的域名。該-H選項不能與使用-F選項。
-F
指定fqdn.fqdn選項以發送到DHCP服務器。此選項不能與-H選項一起使用。該fqdn.fqdn選項必須指定客戶端主機，該服務器可以使用動態DNS更新的完整域名。
-V
指定vendor-class-identifier選項以發送到DHCP服務器。
-R [ ， ...]
指定客戶端要從服務器請求的選項列表。選項列表必須是單個字符串，由至少由一個命令分隔的選項名稱和可選的空格字符組成。默認選項列表為：
subnet-mask, broadcast-address, time-offset, routers, domain-name, domain-name-servers, host-name, nis-domain, nis-servers, ntp-servers, interface-mtu
該-R選項不附加選項為默認請求時，它會覆蓋默認請求列表。如果您要請求默認請求列表之外的其他選項，請記住這一點。您必須為-R參數指定所有選項名稱。
-timeout
指定在未收到任何響應時dhclient決定無法聯系DHCP服務器的時間。
-v
啟用詳細日志消息。
如果客戶端被信號殺死（例如，在關閉或重新啟動時），則它將不會在退出時執行dhclient-script。但是，如果使用-r或-x正常關閉客戶端，則會在關閉時執行dhclient-script，具體原因是需要調用環境表中設置的腳本。
奧馬皮
DHCP客戶端提供了一些在運行時對其進行控制而不停止它的功能。使用OMAPI（一種用于處理遠程對象的API）提供此功能。OMAPI客戶端使用TCP / IP連接到客戶端，進行身份驗證，然后可以檢查客戶端的當前狀態并對其進行更改。
用戶程序應該直接使用dhcpctl API或OMAPI本身，而不是直接實現基礎的OMAPI協議。Dhcpctl是一個包裝程序，用于處理OMAPI不會自動執行的一些內務處理工作。您想要使用客戶端執行的大多數操作都可以直接使用omshell命令完成，而不必編寫特殊的程序。
控制對象
控制對象使您可以關閉客戶端，釋放其持有的所有租約并刪除其可能添加的任何DNS記錄。它還允許您暫停客戶端-這將取消配置客戶端正在使用的所有接口。然后，您可以重新啟動它，這將導致它重新配置這些接口。通常，您會先使客戶端暫停，然后再進入休眠模式或在便攜式計算機上睡覺。重新上電后，您便可以恢復它。這樣，可以在計算機處于休眠或睡眠狀態時關閉PC卡，然后在計算機退出休眠或睡眠狀態后將其重新初始化為以前的狀態。
控制對象具有一個屬性-狀態屬性。要關閉客戶端，請將其state屬性設置為2。它將自動執行DHCPRELEASE。要暫停它，請將其state屬性設置為3。要恢復它，請將其state屬性設置為4。
dhclient [ -4 | -6 ] [ -S ] [ -N [ -N... ] ] [ -T [ -T... ] ] [ -P [ -P... ] ] [ -p port ] [ -d ] [ -e VAR=value ] [ -q ] [ -1 ] [ -r | -x ] [ -lf lease-file ] [ -pf pid-file ] [ -cf config-file ] [ -sf script-file ] [ -s server ] [ -g relay ] [ -n ] [ -nc ] [ -nw ] [ -w ] [ -B ] [ -I dhcp-client-identifier ] [ -H host-name ] [ -F fqdn.fqdn ] [ -V vendor-class-identifier ] [ -R request-option-list ] [ -timeout timeout ] [ -v ] [ --version ] [ if0 [ ...ifN ] ]Options
-4
Use the DHCPv4 protocol to obtain an IPv4 address and configuration parameters (default).
-6
Use the DHCPv6 protocol to obtain whatever IPv6 addresses are available along with configuration parameters. The functionality of DHCPv6 mode may be modified with the -S, -T, and -N options.
-S
Perform an information-only request over DHCPv6 to get stateless configuration parameters. It is not recommended to combine this option with the -N, -P, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-N
Perform a normal (IA_NA) address query over DHCPv6. It is not recommended to combine this option with the -P, -S, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-T
Perform a temporary (IA_TA) address query over DHCPv6 (disables normal address query). It is not recommended to combine this option with the -N, -P, or -S options or share lease files between different modes of operation. Only valid with the -6 option.
-P
Enable IPv6 prefix delegation (disables normal address query). It is not recommended to combine this option with the -N, -S, or -T options or share lease files between different modes of operation. Only valid with the -6 option.
-p
The UDP port number the DHCP client should listen and transmit. If unspecified, dhclient uses the default port 68. This option is mostly useful for debugging purposes. If a different port is specified for the client to listen and transmit on, the client will also use a different destination port: one less than the specified port.
-d
Force dhclient to run as a foreground process. This is useful when running the client under a debugger, or when running it out of inittab on System V systems.
-e VAR=value
Define additional environment variables for the environment where dhclient-script executes. You may specify multiple -e options on the command line. For example: -e IF_METRIC=1
-q
Suppress all terminal and log output except error messages.
-1
Try once to get a lease. One failure, exit with code 2.
-r
Tell dhclient to release the current lease it has from the server. This is not required by the DHCP protocol, but some ISPs require their clients to notify the server if they wish to release an assigned IP address.
-lf
Path to the lease database file. If unspecified, the default /var/lib/dhclient/dhclient.leases is used.
-pf
Path to the process ID file. If unspecified, the default /var/run/dhclient.pid is used.
-cf
Path to the client configuration file. If unspecified, the default /etc/dhcp/dhclient.conf is used.
-sf
Path to the network configuration script invoked by dhclient when it gets a lease. If unspecified, the default /sbin/dhclient-script is used.
-s
Specify the server IP address or fully qualified domain name to transmit DHCP protocol messages. Normally, dhclient transmits these messages to 255.255.255.255 (the IP limited broadcast address). Overriding this is mostly useful for debugging purposes.
-g
Only for debugging. Set the giaddr field of all packets the client sends to the IP address specified. This should not be expected to work in any consistent or useful way.
-n
Do not configure any interfaces. Most useful combined with the -w option.
-nc
Do not drop capabilities.
Normally, if dhclient was compiled with libcap-ng support, dhclient drops most capabilities immediately upon startup. While more secure, this greatly restricts the additional actions that hooks in dhclient-script can take. (For example, any daemons that dhclient-script starts or restarts will inherit the restricted capabilities as well, which may interfere with their correct operation.) Thus, the -nc option can be used to prevent dhclient from dropping capabilities.
The -nc option is ignored if dhclient was not compiled with libcap-ng support.
-nw
Become a daemon process immediately (nowait) rather than waiting until an IP address is acquired.
-w
Keep running even if no network interfaces are found. The omshell program can be used to notify the client when a network interface is added or removed so it can attempt to configure an IP address on that interface.
-B
Set the BOOTP broadcast flag in request packets so servers will always broadcast replies.
-I
Specify the dhcp-client-identifier option to send to the DHCP server.
-H
Specify the host-name option to send to the DHCP server. The host-name string only contains the client's hostname prefix, to which the server will append the ddns-domainname or domain-name options, if any, to derive the fully qualified domain name of the client. The -H option cannot be used with the -F option.
-F
Specify the fqdn.fqdn option to send to the DHCP server. This option cannot be used with the -H option. The fqdn.fqdn option must specify the complete domain name of the client host, which the server may use for dynamic DNS updates.
-V
Specify the vendor-class-identifier option to send to the DHCP server.
-R [,...]
Specify the list of options the client is to request from the server. The option list must be a single string consisting of option names separated by at least one command and optional space characters. The default option list is:
subnet-mask, broadcast-address, time-offset, routers, domain-name, domain-name-servers, host-name, nis-domain, nis-servers, ntp-servers, interface-mtu
The -R option does not append options to the default request, it overrides the default request list. Keep this in mind if you want to request an additional option besides the default request list. You have to specify all option names for the -R parameter.
-timeout
Specify the time after which dhclient will decide that no DHCP servers can be contacted when no responses have been received.
-v
Enable verbose log messages.
If the client is killed by a signal (for example at shutdown or reboot), it will not execute the dhclient-script at exit. However, if you shut the client down gracefully with -r or -x it will execute dhclient-script at shutdown with the specific reason for calling the script set in the environment table.
Omapi
The DHCP client provides some ability to control it while it is running, without stopping it. This capability is provided using OMAPI, an API for manipulating remote objects. OMAPI clients connect to the client using TCP/IP, authenticate, and can then examine the client's current status and make changes to it.
Rather than implementing the underlying OMAPI protocol directly, user programs should use the dhcpctl API or OMAPI itself. Dhcpctl is a wrapper that handles some of the housekeeping chores that OMAPI does not do automatically. Most things you'd want to do with the client can be done directly using the omshell command, rather than having to write a special program.
The control object
The control object allows you to shut the client down, releasing all leases that it holds and deleting any DNS records it may have added. It also allows you to pause the client - this unconfigures any interfaces the client is using. You can then restart it, which causes it to reconfigure those interfaces. You would normally pause the client before going into hibernation or sleep on a laptop computer. You would then resume it after the power comes back. This allows PC cards to be shut down while the computer is hibernating or sleeping, and then reinitialized to their previous state once the computer comes out of hibernation or sleep.
The control object has one attribute - the state attribute. To shut the client down, set its state attribute to 2. It will automatically do a DHCPRELEASE. To pause it, set its state attribute to 3. To resume it, set its state attribute to 4.
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dhclient 例子
更新主以太網設備的動態分配的IP地址。
Renews the dynamically-assigned IP address of a primary Ethernet device.
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其他命令行
date | du | dpost | dmesg | dirname | dircmp | dd | deluser | depmod | deroff | df | diff | dos2unix | dig |