LPI Linux Certification in a Nutshell (34 page)

FHS offers the Linux community an excellent resource that
assures consistency across distributions and other operating systems. In
practice, however, file location problems can be frustrating, and the
need arises to find files in the system quickly. These file location
tools are required for Exam 101:
which, find, locate,
whereis
, and
type
.

which
uses the
PATH
variable to locate executable files.
find
searches specified areas in the filesystem.
whereis
searches in a small subset of common
directories.
locate
offers a quick alternative to
find
for filename searches and is suited for
locating files that are not moved around in the filesystem. Without a
fresh database to search,
locate
is not suitable
for files recently created or renamed.

which

which
command

Determine the location of
command
and display the full pathname of
the executable program that the shell would launch to execute it.
which
searches only the user’s path.

Determine the shell that would be started by entering the
tcsh
command:

#
which tcsh
/bin/tcsh

which
is small and does only one thing:
determines what executable program will be found and called by the
shell. Such a search is particularly useful if you’re having trouble
with the setup of your
PATH
environment variable or if you are creating a new version of an
existing utility and want to be certain you’re executing the
experimental version.

find

find
paths expression

Locate files that match an
expression
starting at
paths
and continuing recursively. The
find
command has a rich set of
expression
directives for locating just
about anything in the
filesystem
.

To find files by name located in the
/usr
directory hierarchy that might have something to do with the
csh
shell or its variants, you might use the
-name
filename
directive:

#
find /usr -name "*csh*"
/usr/bin/sun-message.csh
/usr/doc/tcsh-6.08.00
/usr/doc/tcsh-6.08.00/complete.tcsh
/usr/doc/vim-common-5.3/syntax/csh.vim
/usr/man/man1/tcsh.1
/usr/share/apps/ktop/pics/csh.xpm
/usr/share/apps/ktop/pics/tcsh.xpm
/usr/share/emacs/20.3/etc/emacs.csh
/usr/share/vim/syntax/csh.vim
/usr/src/linux-2.2.5/fs/lockd/svcshare.c

Some of these results are clearly related to
csh
or to
tcsh
, whereas
others are questionable. In addition, this command may take a while
because
find
must traverse the
entire
/usr
hierarchy, examining each filename
for a match. This example demonstrates that if filename wildcards
are used, the entire string must be quoted to prevent expansion by
the shell prior to launching
find
.

find
is among the most useful commands in
the Linux administrator’s toolkit and has a variety of useful
options.
find
is handy in certain cases. For
example:

Refer to
Chapter 6
, for
additional information on the
find
command.

locate

locate
patterns

Locate files whose names match one or more
patterns
by searching an index of files
previously created.

Locate files by name in the entire directory hierarchy that
might have something to do with the
csh
shell
or its variants:

#
locate csh
/home/jdean/.tcshrc
/root/.cshrc
/root/.tcshrc
/usr/bin/sun-message.csh
/usr/doc/tcsh-6.08.00
/usr/doc/tcsh-6.08.00/FAQ
/usr/doc/tcsh-6.08.00/NewThings
/usr/doc/tcsh-6.08.00/complete.tcsh
/usr/doc/tcsh-6.08.00/eight-bit.txt
/usr/doc/vim-common-5.3/syntax/csh.vim
/usr/man/man1/tcsh.1
/usr/share/apps/ktop/pics/csh.xpm
/usr/share/apps/ktop/pics/tcsh.xpm
/usr/share/emacs/20.3/etc/emacs.csh
/usr/share/vim/syntax/csh.vim
/usr/src/linux-2.2.5/fs/lockd/svcshare.c
/etc/csh.cshrc
/etc/profile.d/kde.csh
/etc/profile.d/mc.csh
/bin/csh
/bin/tcsh

The
locate
command must have a recent
database to search, and that database must be updated periodically
to incorporate changes in the filesystem. If the database is stale,
using
locate
yields a warning:

#
locate tcsh
locate: warning: database /var/lib/slocate/slocate.db' is more \
than 8 days old

updatedb

updatedb [
options
]

Refresh (or create) the
slocate
database in
/var/lib/slocate/slocate.db
.

Refresh the
slocate
database, excluding
files in temporary locations:

#
updatedb -e "/tmp,/var/tmp,/usr/tmp,/afs,/net,/proc"

updatedb
is typically executed
periodically via
cron
.

Some Linux distributions (Debian, for example) come with a
version of
updatedb
that accepts additional
options that can be specified on the command line:

These options modify the behavior of
updatedb
on some Linux systems by prohibiting
the parsing of certain filesystem locations and by adding others.
There are a few more of these options than those listed here, but
these three are special in that they can also be specified through
the use of environment variables set prior to
updatedb
execution. The variables are
NETPATHS
,
PRUNEPATHS
, and
PRUNEFS
. These variables and the options
to
updatedb
are discussed here because this
Objective makes specific mention of
updatedb.conf
, a sort of control file for
updatedb
. Despite its name,
updatedb.conf
isn’t really a configuration
file, but rather a fragment of a Bourne shell script that sets these
environment variables.
Example 7-2
shows a sample
updatedb.conf
file.

# This file sets environment variables used by updatedb
# filesystems which are pruned from updatedb database:
PRUNEFS="NFS nfs afs proc smbfs autofs auto iso9660"
export PRUNEFS
# paths which are pruned from updatedb database:
PRUNEPATHS="/tmp /usr/tmp /var/tmp /afs /amd /alex"
export PRUNEPATHS
# netpaths which are added:
NETPATHS="/mnt/fs3"
export NETPATHS

In this example, the
PRUNEFS
and
PRUNEPATHS
variables cause
updatedb
to ignore types of filesystems and
particular paths, respectively.
NETPATHS
is used to add network paths from
remote directory
/mnt/fs3
.

updatedb.conf
doesn’t directly control
updatedb
, but eliminates the need for lengthy
options on the
updatedb
command line, which can
make
crontab
files a bit cleaner.

whereis

whereis [
options
]
filename

whereis
locates source/binary and
manuals sections for specified files.

#
whereis ls
ls: /bin/ls /usr/share/man/man1p/ls.1p.gz /usr/share/man/man1/ls.1.gz

type

type [
options
]
filename

type
is not actually a separate
program, but a built-in part of the
bash
shell.
type
will tell you how a
filename
would be interpreted if used as
a command name.

#
type ls
ls is aliased to `ls --color=auto'
#
type grep
grep is hashed (/bin/grep)
#
type foo
-bash: type: foo: not found