23.4 重新編譯 “world”

23.4.7.1 保留編譯的紀錄

建議養成好習慣，把執行 make(1) 時產生的紀錄存起來。 這樣若有哪邊出錯，就會有錯誤訊息的紀錄。 雖然單單這樣， 你可能不知道如何分析是哪邊出了岔，但若把你問題記錄貼到 FreeBSD 相關的 mailing list 就可以有人可以幫忙看是怎麼一回事情。

最簡單的方是就是用 script(1) 指令，並加上參數 (你想存放記錄的檔案位置、檔名)即可。 這步驟應該在重新編譯系統時就要作，然後在完成編譯後輸入 exit 即可離開。

# script /var/tmp/mw.out
Script started, output file is /var/tmp/mw.out   
# make TARGET
... compile, compile, compile ...     
# exit
Script done, ...

對了，還有一點儘量別把檔案存到 /tmp 目錄內。 因為重開機之後， 這目錄內的東西都會被清空。 比較妥善的地方是 /var/tmp (如上例所示) 或者是 root 的家目錄。

23.4.7.2 編譯 Base System

首先請先切換到 /usr/src 目錄：

# cd /usr/src

(當然，除非你把 source code 放到其他地方，若真是這樣， 就切換到那個目錄即可)。

使用 make(1) 指令來重新編譯 world。 這指令會從 Makefile 檔(這檔會寫 FreeBSD 的程式該如何重新編譯、以哪些順序來編譯等等)去讀取相關指令。

一般下指令的格式如下：

# make -x -DVARIABLE target

在這個例子，-x 是你想傳給 make(1) 的選項，細節說明請參閱 make(1) 說明， 裡面有相關範例說明。

-DVARIABLE 則是把變數設定傳給 Makefile。 這些變數會控制 Makefile 的行為。 這些設定與 /etc/make.conf 的變數設定是一樣， 只是另一種設定方式而已。

# make -DNO_PROFILE target

上面的例子則是另一種設定方式，也就是哪些不要。 這個例子中的意思是不去編譯 profiled libraries，效果就如同設定在 /etc/make.conf 的

NO_PROFILE=    true    #    Avoid compiling profiled libraries

target 則是告訴 make(1) 該去做哪些。 每個 Makefile 都會定義不同的 “targets”，然後依您所給的 target 就會決定會做哪些動作 。

某些 targets 會在 Makefile 列出，但是不一定是給您使用的。 Instead, they are used by the build process to break out the steps necessary to rebuild the system into a number of sub-steps.

通常，您不需要給 make(1) 任何參數，所以您的指令看起來像這樣：

# make target

這裡的 target可以是一個或多個建立選項。 第一個 target 應該都要是 buildworld。

正如其名，buildworld 建立一個完整的系統放在 /usr/obj； 而另一個 target installworld 則將這些東西安裝到機器上。

將選項獨立有兩個好理由。第一，it allows you to do the build safe in the knowledge that no components of your running system will be affected. The build is “self hosted”. Because of this, you can safely run buildworld on a machine running in multi-user mode with no fear of ill-effects. It is still recommended that you run the installworld part in single user mode, though.

Secondly, it allows you to use NFS mounts to upgrade multiple machines on your network. If you have three machines, A, B and C that you want to upgrade, run make buildworld and make installworld on A. B and C should then NFS mount /usr/src and /usr/obj from A, and you can then run make installworld to install the results of the build on B and C.

Although the world target still exists, you are strongly encouraged not to use it.

Run

# make buildworld

It is possible to specify a -j option to make which will cause it to spawn several simultaneous processes. This is most useful on multi-CPU machines. However, since much of the compiling process is IO bound rather than CPU bound it is also useful on single CPU machines.

On a typical single-CPU machine you would run:

# make -j4 buildworld

make(1) will then have up to 4 processes running at any one time. Empirical evidence posted to the mailing lists shows this generally gives the best performance benefit.

If you have a multi-CPU machine and you are using an SMP configured kernel try values between 6 and 10 and see how they speed things up.

23.4.7.3 Timings

Many factors influence the build time, but fairly recent machines may only take a one or two hours to build the FreeBSD-STABLE tree, with no tricks or shortcuts used during the process. A FreeBSD-CURRENT tree will take somewhat longer.

23.4.11.1 mergemaster

Contributed by Tom Rhodes.

The mergemaster(8) utility is a Bourne script that will aid you in determining the differences between your configuration files in /etc, and the configuration files in the source tree /usr/src/etc. This is the recommended solution for keeping the system configuration files up to date with those located in the source tree.

To begin simply type mergemaster at your prompt, and watch it start going. mergemaster will then build a temporary root environment, from / down, and populate it with various system configuration files. Those files are then compared to the ones currently installed in your system. At this point, files that differ will be shown in diff(1) format, with the + sign representing added or modified lines, and - representing lines that will be either removed completely, or replaced with a new line. See the diff(1) manual page for more information about the diff(1) syntax and how file differences are shown.

mergemaster(8) will then show you each file that displays variances, and at this point you will have the option of either deleting the new file (referred to as the temporary file), installing the temporary file in its unmodified state, merging the temporary file with the currently installed file, or viewing the diff(1) results again.

Choosing to delete the temporary file will tell mergemaster(8) that we wish to keep our current file unchanged, and to delete the new version. This option is not recommended, unless you see no reason to change the current file. You can get help at any time by typing ? at the mergemaster(8) prompt. If the user chooses to skip a file, it will be presented again after all other files have been dealt with.

Choosing to install the unmodified temporary file will replace the current file with the new one. For most unmodified files, this is the best option.

Choosing to merge the file will present you with a text editor, and the contents of both files. You can now merge them by reviewing both files side by side on the screen, and choosing parts from both to create a finished product. When the files are compared side by side, the l key will select the left contents and the r key will select contents from your right. The final output will be a file consisting of both parts, which can then be installed. This option is customarily used for files where settings have been modified by the user.

Choosing to view the diff(1) results again will show you the file differences just like mergemaster(8) did before prompting you for an option.

After mergemaster(8) is done with the system files you will be prompted for other options. mergemaster(8) may ask if you want to rebuild the password file and will finish up with an option to remove left-over temporary files.

23.4.11.2 Manual Update

If you wish to do the update manually, however, you cannot just copy over the files from /usr/src/etc to /etc and have it work. Some of these files must be “installed” first. This is because the /usr/src/etc directory is not a copy of what your /etc directory should look like. In addition, there are files that should be in /etc that are not in /usr/src/etc.

If you are using mergemaster(8) (as recommended), you can skip forward to the next section.

The simplest way to do this by hand is to install the files into a new directory, and then work through them looking for differences.

You need to build a dummy set of directories to install the new /etc and other files into. /var/tmp/root is a reasonable choice, and there are a number of subdirectories required under this as well.

# mkdir /var/tmp/root
# cd /usr/src/etc
# make DESTDIR=/var/tmp/root distrib-dirs distribution

This will build the necessary directory structure and install the files. A lot of the subdirectories that have been created under /var/tmp/root are empty and should be deleted. The simplest way to do this is to:

# cd /var/tmp/root
# find -d . -type d | xargs rmdir 2>/dev/null

This will remove all empty directories. (Standard error is redirected to /dev/null to prevent the warnings about the directories that are not empty.)

/var/tmp/root now contains all the files that should be placed in appropriate locations below /. You now have to go through each of these files, determining how they differ with your existing files.

Note that some of the files that will have been installed in /var/tmp/root have a leading “.”. At the time of writing the only files like this are shell startup files in /var/tmp/root/ and /var/tmp/root/root/, although there may be others (depending on when you are reading this). Make sure you use ls -a to catch them.

The simplest way to do this is to use diff(1) to compare the two files:

# diff /etc/shells /var/tmp/root/etc/shells

This will show you the differences between your /etc/shells file and the new /var/tmp/root/etc/shells file. Use these to decide whether to merge in changes that you have made or whether to copy over your old file.