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Test Your Knowledge in Computers #914
Difficulty: Medium
In bash, grep -v -e '^[[:space:]]*$' file.txt will filter all the blank lines from file.txt and save the results in a file called file.txt.
True or False?
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resolvconf(8) [netbsd man page]

RESOLVCONF(8)						      System Manager's Manual						     RESOLVCONF(8)

NAME
resolvconf -- a framework for managing multiple DNS configurations SYNOPSIS
resolvconf -I resolvconf [-m metric] [-p] -a interface <file resolvconf [-f] -d interface resolvconf -il pattern resolvconf -u DESCRIPTION
resolvconf manages resolv.conf(5) files from multiple sources, such as DHCP and VPN clients. Traditionally, the host runs just one client and that updates /etc/resolv.conf. More modern systems frequently have wired and wireless interfaces and there is no guarantee both are on the same network. With the advent of VPN and other types of networking daemons, many things now contend for the contents of /etc/resolv.conf. resolvconf solves this by letting the daemon send their resolv.conf(5) file to resolvconf via stdin(3) with the argument -a interface instead of the filesystem. resolvconf then updates /etc/resolv.conf as it thinks best. When a local resolver other than libc is installed, such as dnsmasq(8) or named(8), then resolvconf will supply files that the resolver should be configured to include. resolvconf can mark an interfaces resolv.conf as private. This means that the name servers listed in that resolv.conf are only used for queries against the domain/search listed in the same file. This only works when a local resolver other than libc is installed. See resolvconf.conf(5) for how to configure resolvconf to use a local name server. When an interface goes down, it should then call resolvconf with -d interface arguments to delete the resolv.conf file for the interface. Here are some more options that resolvconf has:- -I Initialise the state directory /var/run/resolvconf. This only needs to be called if the initial system boot sequence does not auto- matically clean it out; for example the state directory is moved somewhere other than /var/run. If used, it should only be called once as early in the system boot sequence as possible and before resolvconf is used to add interfaces. -f Ignore non existant interfaces. Only really useful for deleting interfaces. -i pattern List the interfaces, optionally matching pattern, we have resolv.conf files for. -l pattern List the resolv.conf files we have. If pattern is specified then we list the files for the interfaces that match it. -m metric Set the metric of the interface when adding it, default of 0. Lower metrics take precedence. This affects the default order of interfaces when listed. -p Marks the interface resolv.conf as private. -u Force resolvconf to update all it's subscribers. resolvconf does not update the subscribers when adding a resolv.conf that matches what it already has for that interface. resolvconf also has some options designed to be used by it's subscribers:- -v Echo variables DOMAINS, SEARCH and NAMESERVERS so that the subscriber can configure the resolver easily. INTERFACE ORDERING
For resolvconf to work effectively, it has to process the resolv.confs for the interfaces in the correct order. resolvconf first processes interfaces from the interface_order list, then interfaces without a metic and that match the dynamic_order list, then interfaces with a met- ric in order and finally the rest in the operating systems lexical order. See resolvconf.conf(5) for details on these lists. IMPLEMENTATION NOTES
If a subscriber has the executable bit then it is executed otherwise it is assumed to be a shell script and sourced into the current environ- ment in a subshell. This is done so that subscribers can remain fast, but are also not limited to the shell language. Portable subscribers should not use anything outside of /bin and /sbin because /usr and others may not be available when booting. Also, it would be unwise to assume any shell specific features. ENVIRONMENT
IF_METRIC If the -m option is not present then we use IF_METRIC for the metric. IF_PRIVATE Marks the interface resolv.conf as private. FILES
/etc/resolvconf.conf Configuration file for resolvconf. /libexec/resolvconf Directory of subscribers which are run every time resolvconf adds, deletes or updates. /libexec/resolvconf/libc.d Directory of subscribers which are run after the libc subscriber is run. /var/run/resolvconf State directory for resolvconf. HISTORY
This implementation of resolvconf is called openresolv and is fully command line compatible with Debian's resolvconf, as written by Thomas Hood. SEE ALSO
resolv.conf(5), resolvconf.conf(5), resolver(3), stdin(3) AUTHORS
Roy Marples <roy@marples.name> BUGS
Please report them to http://roy.marples.name/projects/openresolv resolvconf does not validate any of the files given to it. When running a local resolver other than libc, you will need to configure it to include files that resolvconf will generate. You should con- sult resolvconf.conf(5) for instructions on how to configure your resolver. BSD
May 13, 2011 BSD

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