Hi Branden, On 1/15/23 06:43, G. Branden Robinson wrote:
* Recast summary description to identify relevance of libraries. * Drop `-V` option from synopsis; it doesn't make any sense combined with the operation mode shown, and no other "get out quick" option, including its synonym `--version`, is documented in the synopsis. * Clarify that the "links" manipulated by the program are symbolic. * Discuss caching feature separately from symbolic link management. * Clarify how ldconfig can be run by unprivileged users (probably for troubleshooting). * Recast example of shared library linkage chain and motivate the existence for each link or file. Define term "soname" and present it in lowercase like other Linux man-pages, instead of full caps. * Document auxiliary cache file, which apparently has been described nowhere but a source comment in the original commit 15 years ago. * Document that `-C` implies `-i`. See elf/ldconfig.c:162. * Clarify how `-l` option works (a little). * Drop mention of "quiet mode", which does not seem to exist. * Be explicit that `-p`/`--print-cache` option exits early; i.e., it doesn't undertake ldconfig's primary function. * Document `--usage` and `-?`/`--help` options. * Clarify what `-v`/`--verbose` does. * Clarify that `-V`/`--version` exits early. * Expand description of "ld.so.conf" file to discuss "include" and "hwcap" features. Describe these as "directives" (though the latter died upstream in glibc 2.32 before we got around to documenting it). Document lad.so.conf's comment syntax. * Document handling of leading spaces and empty lines in ld.so.conf. * Document location of auxiliary cache file. Signed-off-by: G. Branden Robinson <g.branden.robinson@xxxxxxxxx> --- man8/ldconfig.8 | 121 +++++++++++++++++++++++++++++++++++++----------- 1 file changed, 95 insertions(+), 26 deletions(-) diff --git a/man8/ldconfig.8 b/man8/ldconfig.8 index 36b891dab..5b671f0a1 100644 --- a/man8/ldconfig.8 +++ b/man8/ldconfig.8 @@ -7,12 +7,12 @@ .\" Change listed order of /usr/lib and /lib .TH ldconfig 8 (date) "Linux man-pages (unreleased)" .SH NAME -ldconfig \- configure dynamic linker run-time bindings +ldconfig \- configure library bindings used by run-time dynamic linker .SH SYNOPSIS .SY /sbin/ldconfig .\" TODO?: -c, --format, -i, --ignore-aux-cache, --print-cache, .\" --verbose, -V, --version, -?, --help, --usage -.RB [ \-nNvVX ] +.RB [ \-nNvX ] .RB [ \-C\~\c .IR cache ] .RB [ \-f\~\c @@ -31,8 +31,10 @@ ldconfig \- configure dynamic linker run-time bindings .YS .SH DESCRIPTION .B \%ldconfig -creates the necessary links and cache to the most recent shared -libraries found in the directories specified on the command line, +creates the necessary symbolic links +to the most recent versions of the shared libraries +found in the directories +specified on the command line, in the file .IR /etc/ld.so.conf , and in the trusted directories, @@ -50,7 +52,8 @@ and .I /usr/lib64 are used for 64-bit libraries. .PP -The cache is used by the run-time linker, +It also maintains a cache +used by the run-time linker, .I ld.so or .IR ld\-linux.so . @@ -61,8 +64,11 @@ determining which versions should have their links updated. .\" 8ee878592c4a642937152c8308b8faef86bcfc40 (2022-07-14) as "obsolete .\" for over twenty years". .B \%ldconfig -should normally be run by the superuser as it may require write -permission on some root owned directories and files. +is normally run by the superuser +since it may require write permission +on some root-owned directories and files. +.RI \%\(lq ldconfig\~\-p \(rq +can be run without such privileges. .PP .B \%ldconfig will look only at files that are named @@ -74,10 +80,7 @@ Other files will be ignored. Also, .B \%ldconfig expects a certain pattern to how the symbolic links are set up, -like this example, -where the middle file -.RB ( libfoo.so.1 -here) is the SONAME for the library: +as in the following. .PP .in +4n .EX @@ -85,8 +88,26 @@ libfoo.so \-> libfoo.so.1 \-> libfoo.so.1.12 .EE .in .PP -Failure to follow this pattern may result in compatibility issues -after an upgrade. +The name +.B libfoo.so +is used when preparing object code that uses shared libraries.
What do you mean by "preparing"? I'd like this to be clearer. It should also be clear the responsibility of library writers, and which files they need to create, and which not.
So the picture is:- libfoo.so is the "linker name", which the static linker uses to find the library at build time. It is a symbolic link that links the linker name to the soname, and it is responsibility of the library writer to create it, usually through ln(1).
- libfoo.so.MAJOR is the "soname". This is the name that will be used as a dependency in the resulting linked binary. Therefore, the dynamic linker will try to load the library per its soname at exec(3) time. The soname is a symbolic link to the real name of the library; it is created by ldconfig(8), and library authors should not create it normally.
- libfoo.so.MAJOR.MINOR is the "real name". This is the actual file name of the library. It contains information about the soname which is used by the static linker to produce a binary that doesn't depend on minor versions, and also used by ldconfig(8) to produce the soname symbolic link.
<https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html> Cheers, Alex
+.B libfoo.so.1 +is the +.I soname +(shared object name) +used at run time, +by which object code locates its shared library dependencies. +.B libfoo.so.1.12 +is the shared library. +This practice enables upward-compatible upgrades of shared libraries; +a change in the version number after the soname indicates that no +\(lqbreak\(rq in the ABI +(application binary interface) +has occurred. +.PP +.B ldconfig +maintains an auxiliary cache file that helps it to avoid re-reading +libraries that have not changed since the last time it was run. .SH OPTIONS .TP .BI \-c\~ fmt @@ -102,9 +123,9 @@ which is one of or .BR \%compat . Since glibc 2.32, +.\" commit cad64f778aced84efdaa04ae64f8737b86f063ab the default is .BR new . -.\" commit cad64f778aced84efdaa04ae64f8737b86f063ab Before that, it was .BR \%compat . @@ -114,6 +135,8 @@ Use .I cache instead of .IR /etc/ld.so.cache . +Implies +.BR \-i . .TP .BI \-f\~ conf Use @@ -151,27 +174,29 @@ links are still updated. .B \-p .TQ .B \-\-print\-cache -Print the lists of directories and candidate libraries stored in -the current cache. +Report the libraries stored in the cache and exit. .TP .BI \-r\~ root Change to and use .I root as the root directory. .TP +.B \-\-usage +Report a terse usage message and exit. +.TP .B \-v .TQ .B \-\-verbose -Verbose mode. -Print current version number, +Operate verbosely; +for each library, +report the current version number, the name of each directory as it is scanned, and any links that are created. -Overrides quiet mode. .TP .B \-V .TQ .B \-\-version -Print program version. +Report program version information and exit. .TP .B \-X Don't update links. @@ -179,26 +204,70 @@ Unless .B \-N is also specified, the cache is still rebuilt. +.TP +.B \-? +.TQ +.B \-\-help +Report a usage message and exit. .SH FILES -.\" FIXME Since glibc-2.3.4, "include" directives are supported in ld.so.conf -.\" -.\" FIXME Since glibc-2.4, "hwcap" directives are supported in ld.so.conf -.PD 0 .TP .I /lib/ld.so is the run-time linker/loader. .TP .I /etc/ld.so.conf +.RS contains a list of directories, one per line, -in which to search for libraries. +in which to search for libraries; +or a multi-word +.I directive +further configuring the run-time linker/loader. +A number sign +.RB ( # ) +introduces a comment that extends to the end of the line; +this character is thus not supported in directives or directory names. +Leading spaces are removed. +Empty lines are ignored. +.PP +Since glibc\~2.3.4, +.\" commit 8e115d80b07f17a11690c108918f847846a752da +a directive in the form +.RS +.EX +include\~\c +.I filename\~\c +\&.\|.\|. +.EE +.RE +is supported; +each +.I filename +is recursively opened and read. +.\" XXX: ...with no detection of cycles! +.I filename +can be a +.BR glob (3) +pattern. +This feature enables libraries or packages to manage shared library +placement in a modular way. +.PP +In glibc\~2.4, +.\" commit ab1d521db39bf4371c7db96e8a0fcd4857ee70ed +a +.B \%hwcap +directive was introduced, +but it is no longer supported as of glibc\~2.32. +.\" commit 31563b68410ff8e9490c5aafca31ec71b38f87a5 +.RE .TP .I /etc/ld.so.cache contains an ordered list of libraries found in the directories specified in .IR /etc/ld.so.conf , as well as those found in the trusted directories. -.PD +.TP +.I /var/cache/ldconfig/aux\-cache +is the auxiliary cache. .SH SEE ALSO .BR ldd (1), .BR ld.so (8)
-- <http://www.alejandro-colomar.es/>
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