Tài liệu Chapter-31-Keeping up to date pptx

In Chapter 32, Updating the system software, we’ll look at how to upgrade FreeBSD to a new release, with particular reference to upgrades to FreeBSD Release 5, and in Chapter 33, Custom

Keeping up to date

In this chapter:

and CVS

the Net

tree

In this chapter:

and CVS

the Net

tree

FreeBSD is constantly changing The average time that elapses between changes to the source tree is in the order of a few minutes Obviously you can’t keep up to date with that pace of change

In the following three chapters we’ll look at how to keep up to date In this chapter, we’ll look at:

• FreeBSD releases: how the FreeBSD project comes to terms with the rapid rate of change, and how it keeps the system stable despite the changes

• How the system sources are stored, and how you can update them

In Chapter 32, Updating the system software, we’ll look at how to upgrade FreeBSD to a

new release, with particular reference to upgrades to FreeBSD Release 5, and in Chapter

33, Custom kernels, we’ll look at building special kernels.

FreeBSD releases and CVS

The FreeBSD project keeps the entire operating system sources in a single master source

tree, called a repository, which is maintained by the Concurrent Versions System, or CVS.

It’s included in most multi–CD-ROM distributions of FreeBSD The repository contains all versions of FreeBSD back to Release 2.0 and the last release from the Computer Sciences Research Group of the University of California at Berkeley, 4.4BSD-Lite, upon which it was based For copyright reasons FreeBSD Release 1 was not included, because

at the time, as the result of the lawsuits described on page 8, it was not permitted to distribute it freely That situation changed in early 2002, but it’s now too late to include FreeBSD Release 1 in the repository

582 Chapter 31: Keeping up to date

CVS is built on top of the Revision Control System, or RCS RCS keeps multiple versions

of files, called re visions, in a single RCS file Each revision has a number indicating its

relationship to the other revisions The oldest revision has the number 1.1, the next oldest has the number 1.2, and so on The RCS file contains the most recent revision of the file along with instructions for creating any other revision

In addition to this linear sequence, it’s possible to update a specific revision in more than one way The obvious way to update revision 1.2 would create revision 1.3; but it’s also

possible to create branches, which get numbers like 1.2.1.1 Updating revision 1.2.1.1

would create revision 1.2.1.2, and so on By contrast, the revisions with a two-part

number are collectively called the trunk of the tree.

Symbolic names or tags

In addition to the numeric identifiers, each of which relates only to a single file, RCS

allows you to attach symbolic names to specific revisions CVS generally calls these names tags, and that’s the term you’ll see most often FreeBSD uses tags to indicate the

revisions corresponding to a particular release For example, in the directory

/usr/src/sys/kern, revision 1.13 of kern_clock.c, revision 1.12 of kern_fork.c and revision 1.21.4.1 of kern_exec.c participate inRELENG_2_1_0_RELEASE We’ll look at tags in more detail on page 588

RCS stores its files either in the same directory as the working files it is tracking, or in a subdirectory RCS if it exists To avoid file name conflicts, RCS appends the characters ,v

to the RCS file, so the working file main.c would correspond to the RCS file main.c,v For more details of RCS, see the man page.

CVS is an extension to RCS that allows concurrent access, making it more suitable for projects involving more than one person Unlike RCS, it stores its RCS files in a separate directory hierarchy, called a repository Each directory in the working tree contains a subdirectory CVS with information on the location of the repository, the revisions of the

working files and a tag if the revision isn’t on the trunk

If you’re a serious developer, there are a number of advantages to keeping a copy of the repository If you’re a casual user, it’s probably overkill

FreeBSD releases

There are four main versions of FreeBSD, each intended for use by different people:

FreeBSD-RELEASE

Fr eeBSD-RELEASE is the latest version of FreeBSD that has been released for general

use It contains those new features that are stable, and it has been through extensive testing You can get it on CD-ROM FreeBSD-RELEASEs are given a release number that uniquely identifies them, such as 5.0 There are three or four releases a year A new branch is made for each release of FreeBSD

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FreeBSD releases 583

FreeBSD-STABLE

Fr eeBSD-STABLE is an updated version of FreeBSD-RELEASE to which all possible

bug fixes hav e been applied, to make it as stable as possible Fixes are made on a daily basis It is based on the same source branch as FreeBSD-RELEASE, so it has all the features and fewer bugs It may contain additional features, but new features are tested in the-CURRENTbranch first

Due to the frequent updates, FreeBSD-STABLE is not available on CD-ROM

Security fix releases

Despite the name, FreeBSD-STABLE is subject to some problems Every change to a source tree has the potential to go wrong In many cases, you’re more interested in keeping your system running than you are in getting minor bug fixes FreeBSD also maintains a second ‘‘stable’’ branch consisting of the release and only very important bug fixes, including security updates This branch does not have a well-defined name, but it’s

generally referred to as the security branch.

FreeBSD-CURRENT

Fr eeBSD-CURRENT is the very latest version of FreeBSD, located on the trunk of the

tree All new dev elopment work is done on this branch of the tree FreeBSD-CURRENT

is an ever-changing snapshot of the working sources for FreeBSD, including work in progress, experimental changes and transitional mechanisms that may or may not be present in the next official release of the software Many users compile almost daily from FreeBSD-CURRENT sources, but there are times when the sources are uncompilable, or when the system crashes frequently The problems are always resolved, but others can take their place On occasion, keeping up with FreeBSD-CURRENT can be a full-time business If you use-CURRENT, you should be prepared to spend a lot of time keeping

the system running The following extract from the RCS log file for /usr/src/Makefile

should give you a feel for the situation:

$ cvs log Makefile

revision 1.152

date: 1997/10/06 09:58:11; author: jkh; state: Exp; lines: +41 -13

Hooboy!

Did I ever spam this file good with that last commit Despite 3

reviewers, we still managed to revoke the eBones fixes, TCL 8.0 support,

libvgl and a host of other new things from this file in the process of

parallelizing the Makefile DOH! I think we need more pointy hats - this

particular incident is worthy of a small children’s birthday party’s worth of pointy hats ;-)

I certainly intend to take more care with the processing of aged diffs

in the future, even if it does mean reading through 20K’s worth of them.

I might also be a bit more anal about asking for more up-to-date changes

before looking at them ;)

This example also shows the list of the symbolic names for this file, and their corresponding revision numbers There is no symbolic name for-CURRENT, because it is

584 Chapter 31: Keeping up to date

located on the trunk That’s the purpose of the linehead:, which shows that at the time

of this example, the-CURRENTrevision of this file was 1.270

So why use-CURRENT? The main reasons are:

• You might be doing development work on some part of the source tree Keeping

‘‘current’’ is an absolute requirement

• You may be an active tester, which implies that you’re willing to spend time working through problems to ensure that FreeBSD-CURRENT remains as sane as possible You may also wish to make topical suggestions on changes and the general direction

of FreeBSD

• You may just want to keep an eye on things and use the current sources for reference purposes

People occasionally have other reasons for wanting to use FreeBSD-CURRENT The

following are not good reasons:

• They see it as a way to be the first on the block with great new FreeBSD features This is not a good reason, because there’s no reason to believe that the features will stay, and there is good reason to believe that they will be unstable

• They see it as a quick way of getting bug fixes In fact, it’s a way of testing bug fixes.

Bug fixes will be retrofitted into the -STABLE branch as soon as they hav e been properly tested

• They see it as the newest officially supported release of FreeBSD This is incorrect:

FreeBSD-CURRENT is not officially supported The support is provided by the

users

If you do decide to use-CURRENT, read the suggestions on page 621

Snapshots

FreeBSD-CURRENT is available in the form of ISO (CD-ROM) images From time to

time, at irregular intervals when the tree is relatively stable, the release team makes a

snapshot release from the-CURRENTsource tree They are also available on CD-ROM from some vendors; check the online handbook for details This is a possible alternative

to online updates if you don’t want the absolute latest version of the system

Getting updates from the Net

There are a number of possibilities to keep up with the daily modifications to the source tree The first question is: how much space do you want to invest in keeping the sources? Table 31-1 shows the approximate space required by different parts of the sources Note that the repository keeps growing faster than the source tree, because it includes all old revisions as well

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Getting updates from the Net 585

Table 31-1: Approximate source tree sizes

Component Size (MB)

Source tree /usr/src/sys 110

The size of /usr/src/sys includes the files involved in a single kernel build You can

remove the entire kernel build directory, but if you want to be able to analyze a panic

dump, you should keep the kernel.debug file in the kernel build directory This changes the size of /usr/src as well, of course The other object files get built in the directory /usr/obj Again, you can remove this directory tree entirely if you want, either with the

rm command or with make clean Similarly, the size of /usr/ports includes a few

ports It will, of course, grow extremely large (many gigabytes) if you start porting all available packages

If you’re maintaining multiple source trees (say, for different versions), you still only need one copy of the repository

CVSup

CVSup is a software package that distributes updates to the repository You can run the client at regular intervals—for example, with cron (see page 151) to update your

repository

To get started with CVSup, you need the following:

• A source tree or repository, which doesn’t hav e to be up to date This is not absolutely necessary, but the initial setup will be faster if you do it this way

• A copy of the cvsup program Install it with pkg_add from the CD-ROM (/cdrom/packages/Latest/cvsup.tbz).

• A cvsupfile, a command file for cvsup We’ll look at this below.

• A mirror site from which you can load or update the repository We’ll discuss this

below as well

The cvsupfile contains a description of the packages you want to download You can find

all the details in the online handbook, but the following example shows a reasonably normal file:

586 Chapter 31: Keeping up to date

*default release=cvs

*default host=cvsup9.freebsd.org

*default base=/src/cvsup

*default prefix=/home/ncvs

*default delete

*default use-rel-suffix

*default compress

src-all

ports-all

doc-all

The lines starting with *default specify default values; the lines that do not are collections that you want to track This file answers these implicit questions:

• Which files do you want to receive? These are the names of the collections in the last

three lines: all of the sources, ports and documentation

• Which versions of them do you want? By default, you get updates to the repository

If you want a specific version, you can write:

*default tag=version

version is a release tag that identifies the version you want, or (a period) to represent the-CURRENTversion We’ll discuss release tags on page 588

Alternatively, you might ask for a version as of a specific date For example:

*default date=97.09.13.12.20

This would specify that you want the version as it was on 13 September 1997 at 12:20 In this case, version defaults to.(a period)

• Where do you want to get them from? Tw o parameters answer this question:

host=cvsup9.freebsd.orgspecifies the name of the host from which to load the files, and release=cvs specifies to use the cvs release The release option is

obsolescent, but it’s a good idea to leave it in there until it is officially removed

• Where do you want to put them on your own machine? This question is answered by the line *default prefix=/home/ncvs We’re tracking the repository in this example, so this is the name of the repository If we were tracking a particular release, we would use *default prefix=/usr The collections are called doc, ports and src, so we refer to the parent directory in each case.

• Where do you want to put your status files? This question is answered by the line

*default base=/src/cvsup

In addition, the file contains three other lines *default deletemeans that cvsup may

delete files where necessary Otherwise you run the risk of accumulating obsolete files

*default compressenables compression of the data transmitted, and*default use-rel-suffixspecifies how cvsup should handle list files It’s not well-documented, but

it’s necessary Don’t worry about it

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Which CVSup server?

In this example, we’ve chosen one of the backup US servers, cvsup9.FreeBSD.org In

practice, this may not be the best choice A large number of servers are spread around the world, and you should choose the one topographically closest to you This isn’t the same thing as being geographically closest—I live in Adelaide, South Australia, and some ISPs

in the same city are further away on the Net than many systems in California Look on

the web site http://www.FreeBSD.org for an up-to-date list.

Running cvsup

cvsup is a typical candidate for a cron job I rebuild the-CURRENTtree every morning at

3 am To do so, I have the following entry in /root/crontab:

# Get the latest and greatest FreeBSD stuff.

0 3 * * * /extract-updates

The file /root/extract-updates contains, amongst other things,

cvsup -g -L2 /src/cvsup/cvs-cvsupfile

/src/cvsup/cvs-cvsupfile is the name of the cvsupfile we looked at above The other parameters to cvsup specify not to use the GUI (-g), and -L2 specifies to produce moderate detail about the actions being performed

Getting individual releases

The example cvsupfile above is useful if you’re maintaining a copy of the repository If

you just want to maintain a copy of the sources of one version, say Release 5.0, use the following file instead:

*default tag=RELENG_5_0_0_RELEASE

*default release=cvs

*default host=cvsup9.freebsd.org

*default base=/usr for /usr/doc, /usr/ports, /usr/src

*default prefix=/home/ncvs

*default delete

*default use-rel-suffix

*default compress

src-all

Be careful with tags They must exist in the repository, or cvsup will replace what you have with nothing: it will delete all the files In our original cvsupfile, we had two

additional sets,ports-alland doc-all These sets don’t hav e the same release tags, so

if you left them in this file, you would lose all the files in the /usr/doc and /usr/ports

directory hierarchies

588 Chapter 31: Keeping up to date

Creating the source tree

If you’re tracking the repository, you’re not finished yet Once you have an up-to-date repository, the next step is to create a source tree By default, the source tree is called

/usr/src, though it’s very common for /usr/src to be a symbolic link to a source tree on a different file system You create the tree with cvs.

Before you check anything out with cvs, you need to know:

1 What do you want to check out? You specify this with a module name, which usually

corresponds with a directory name (for example, src) There are a number of top-level modules, including doc, ports, src and www.

2 Which version do you want to check out? By default, you get the latest version, which is FreeBSD-CURRENT If you want a different version, you need to specify

its tag.

3 Possibly, the date of the last update that you want to be included in the checkout If

you specify this date, cvs ignores any more recent updates This option is often

useful when somebody discovers a recently introduced bug in-CURRENT: you check out the modules as they were before the bug was introduced You specify the date with the-Doption, as we’ll see below

Release tags

FreeBSD identifies releases with two or more numbers separated by periods Each number represents a progressively smaller increment in the functionality of the release The first number is the base release of FreeBSD The number is incremented only when significant functionality is added to the system The second number represents a less significant, but still important difference in the functionality, and the third number is only used when a significant bug requires rerelease of an otherwise unchanged release Before Release 3 of FreeBSD, a fourth number was sometimes also used

Tags for released versions of FreeBSD follow the release numbers For release x.y.z you

would look for the tagRELENG_x_y_z_RELEASE For example, to get the current state

of the FreeBSD 5.0 source tree, you would look for the tagRELENG_5_0_0_RELEASE Tags for the -STABLE branch are simpler: they just have the release number, for example

RELENG_4 The security branch has an additional number, for exampleRELENG_4_7 Some tags diverge from this scheme In particular,CSRGandbsd_44_liteboth refer to the original 4.4BSD sources from Berkeley If you feel like it, you can extract this source tree as well

To find out what tags are available, do:

# cd $CVSROOT/src

# rlog Makefile,v | less

RCS file: /home/ncvs/src/Makefile,v

RCS file: /home/ncvs/src/Makefile,v

Working file: Makefile

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Creating the source tree 589

head: 1.270

branch:

locks: strict

access list:

symbolic names:

RELENG_5_0_0_RELEASE: 1.271 5.0-RELEASE

RELENG_4_7_0_RELEASE: 1.234.2.18 4.7-RELEASE

RELENG_4_7: 1.234.2.18.0.2 4.7 security fixes only

RELENG_4_7_BP: 1.234.2.18 branch point for 4.7

RELENG_4_6_2_RELEASE: 1.234.2.12 4.6.2-RELEASE

RELENG_4_6_1_RELEASE: 1.234.2.12 4.6.1-RELEASE

RELENG_4_6_0_RELEASE: 1.234.2.12 4.6-RELEASE

BETA_2_0: 1.30

ALPHA_2_0: 1.29.0.2

CSRG: 1.1.1

keyword substitution: kv

total revisions: 179; selected revisions: 179

description:

This example shows the same file we saw on page 583 This time we use the rlog command, which is part of RCS, to look at the revision log Normally you’d use cvslog,

but that only works in a checked out source tree

There are a number of ways to tell cvs the name of its repository: if you already have a CVS subdirectory, it will contain files Root and Repository The name of the repository

is in Root, not in Repository When you first check out files, you won’t hav e this

directory, so you specify it, either with the-doption to cvs or by setting theCVSROOT

environment variable As you can see in the example above, it’s convenient to set the environment variable, since you can use it for other purposes as well

The repository contains a number of directories, usually one for each collection you track In our case, we’re tracking the source tree and the Ports Collection, so:

• CVSROOT contains files used by CVS It is not part of the source tree.

• ports contains the Ports Collection.

• src contains the system sources.

The directories ports and src correspond to the directories /usr/ports and /usr/src for a particular release To extract the src tree of the most up-to-date version of

FreeBSD-CURRENT, do the following:

# cd /usr

# cvs co src 2>&1 | tee /var/tmp/co.log

590 Chapter 31: Keeping up to date

To check out any other version, say, everything for Release 4.6, you would enter:

# cd /usr

# cvs co -r RELENG_4_6_RELEASE src 2>&1 | tee /var/tmp/co.log

If you need to check out an older version, for example if there are problems with the most recent version of-CURRENT, you could enter:

# cvs co -D "10 December 2002" src/sys

This command checks out the kernel sources as of 10 December 2002 During checkout,

cvs creates a subdirectory CVS in each directory CVS contains four files We’ll look at typical values when checking out the version of the directory /usr/src/usr.bin/du for Release 4.6, from the repository at /home/ncvs:

• Entries contains a list of the files being maintained in the parent directory, along with

their current versions In our example, it would contain:

/Makefile/1.4.2.1/Sun Jul 2 10:45:29 2000//TRELENG_4_6_0_RELEASE

/du.1/1.15.2.7/Thu Aug 16 13:16:47 2001//TRELENG_4_6_0_RELEASE

/du.c/1.17.2.3/Thu Jul 12 08:46:53 2001//TRELENG_4_6_0_RELEASE

D

Note that cvs prepends aTto the version name

• Repository contains the name of the directory in the repository that corresponds to the current directory This corresponds to $CVSROOT/directory In our example, it

would containsrc/usr.bin/du

• Root contains the name of the root of the repository In our example, it would

contain/home/ncvs

• Ta g contains the version tag of the source tree This is the RCS tag prefixed by aT

In this case, it isTRELENG_4_6_0_RELEASE

cvs co produces a lot of output—at least one line for each directory, and one line for each

file it checks out Here’s part of a typical output:

U src/usr.sbin/mrouted/rsrr_var.h

U src/usr.sbin/mrouted/vif.c

U src/usr.sbin/mrouted/vif.h

cvs checkout: Updating src/usr.sbin/mrouted/common

U src/usr.sbin/mrouted/common/Makefile

cvs checkout: Updating src/usr.sbin/mrouted/map-mbone

U src/usr.sbin/mrouted/map-mbone/Makefile

cvs checkout: Updating src/usr.sbin/mrouted/mrinfo

U src/usr.sbin/mrouted/mrinfo/Makefile

cvs checkout: Updating src/usr.sbin/mrouted/mrouted

U src/usr.sbin/mrouted/mrouted/Makefile

cvs checkout: Updating src/usr.sbin/mrouted/mtrace

U src/usr.sbin/mrouted/mtrace/Makefile

cvs checkout: Updating src/usr.sbin/mrouted/testrsrr

U src/usr.sbin/mrouted/testrsrr/Makefile

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