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Archive for the ‘bash’ Category

firewalld: show interfaces with their zone details and show zones in use

Posted by jpluimers on 2021/08/26

A while ago openSUSE switched to firewalld as a fronte-end for iptables. Tumbleweed was first in 2018, so I wrote a reminder: On my research list: migrate from OpenSuSE SuSEfirewall2 to firewalld « The Wiert Corner – irregular stream of stuff.

The core concept of firewalld is zones, which some people find hard to understand: [] Firewalld on Leap 15 – why is it so complicated ? : openSUSE.

Another concept is interfaces and how they bind to zones. [Wayback] Masquerading and Firewalls | Security Guide | openSUSE Leap 15.2 shows more of that.

The final concept is services that bind one or more aspects (like ports or addresses) to a service name [Wayback] Documentation – Manual Pages – firewalld.service | firewalld.

Other interesting bits of information:

Below are some examples on what I learned, especially finding details about active interfaces and the zones they are bound to.

All of them are based on:

  • the xargs shell trick (I known you can do some of them without the trick, but I try to use common patterns in my solution so I do not have to remember which boundary case fails
  • the echo -n trick to skip the newline output
  • the [WayBack] firewall-cmd options (which kind of care commands)
    • --get-active-zones:

      Print currently active zones altogether with interfaces and sources used in these zones. Active zones are zones, that have a binding to an interface or source. The output format is:

        interfaces: interface1 interface2 ..
        sources: source1 ..
        interfaces: interface3 ..
        sources: source2 ..

      If there are no interfaces or sources bound to the zone, the corresponding line will be omitted.

    • --list-interfaces:

      List interfaces that are bound to zone zone as a space separated list. If zone is omitted, default zone will be used.

    • --get-zone-of-interface=<zone>:

      Print the name of the zone the interface is bound to or no zone.

    • --info-zone=<zone> (which shows far more information than the manual indicates):

      Print information about the zone zone. The output format is:

        interfaces: interface1 ..
        sources: source1 ..
        services: service1 ..
        ports: port1 ..
        protocols: protocol1 ..
        forward-ports: forward-port1 ..
        source-ports: source-port1 ..
        icmp-blocks: icmp-type1 ..
        rich rules: rich-rule1 ..

Two more notes before the examples:

  1. My first hunch was to use --list-all-zones, but that shows details of all un-used zones as well.
  2. I am not fully sure about the --list-interfaces to list *all* interfaces. I might replace this later with ls /sys/class/net (see [WayBack] linux – List only the device names of all available network interfaces – Super User).

Other useful commands

Besides lising zones and interfaces, you might be interested in services and ports:

# firewall-cmd --list-services
dhcpv6-client ssh
# firewall-cmd --list-ports

List used zones

The first only shows the zone names

# firewall-cmd --list-interfaces | xargs -I {} sh -c 'firewall-cmd --get-zone-of-interface={}'

The second both zones and interfaces:

# firewall-cmd --get-active-zones 
  interfaces: ens192

When there are no bound interfaces

OpenSuSE by default does not bind interfaces to zones; it means any interface uses the default zone. That means the --list-interfaces commands in this blog post fail.

You can check this behaviour by running this command:

# ls /sys/class/net | xargs -I {} sh -c 'echo -n "interface {} has zone " ; firewall-cmd --get-zone-of-interface={} | xargs -I [] sh -c "echo [] ; firewall-cmd --info-zone=[]"'
interface eth0 has zone no zone
interface lo has zone no zone
interface wlan0 has zone no zone


  1. Finding the default zone
    # firewall-cmd --get-default-zone
  2. Details of the default zone
    # firewall-cmd --info-zone=$(firewall-cmd --get-default-zone)
      target: default
      icmp-block-inversion: no
      services: dhcpv6-client ssh
      masquerade: no
      rich rules: 

You can see that here the public zone is marked default which means it binds to any interface that is not bound to a specific zone.

List used zone details

# firewall-cmd --list-interfaces | xargs -I {} sh -c 'firewall-cmd --get-zone-of-interface={} | xargs -I [] sh -c "firewall-cmd --info-zone=[]"'
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: ens192
  services: dhcpv6-client ssh
  masquerade: no
  rich rules: 

List interfaces and their zones:

# firewall-cmd --list-interfaces | xargs -I {} sh -c 'echo -n "interface {} has zone " ; firewall-cmd --get-zone-of-interface={}'
interface ens192 has zone public

List interfaces and their zone details:

# firewall-cmd --list-interfaces | xargs -I {} sh -c 'echo -n "interface {} has zone " ; firewall-cmd --get-zone-of-interface={} | xargs -I [] sh -c "echo [] ; firewall-cmd --info-zone=[]"'
interface ens192 has zone public
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: ens192
  services: dhcpv6-client ssh
  masquerade: no
  rich rules: 

Verifying if dns service is available, then allow it on public

Verify if a DNS is in the enabled services:

# firewall-cmd --list-services
dhcpv6-client ssh

Here no DNS service is enabled, so I need to figure out if any DNS service is available to be enabled.

This lists all the services that can be enabled in a zone:

# firewall-cmd --get-services

On my system, this returned the following list:

RH-Satellite-6 amanda-client amanda-k5-client amqp amqps apcupsd audit bacula bacula-client bb bgp bitcoin bitcoin-rpc bitcoin-testnet bitcoin-testnet-rpc bittorrent-lsd ceph ceph-mon cfengine cockpit condor-collector ctdb dhcp dhcpv6 dhcpv6-client distcc dns dns-over-tls docker-registry docker-swarm dropbox-lansync elasticsearch etcd-client etcd-server finger freeipa-4 freeipa-ldap freeipa-ldaps freeipa-replication freeipa-trust ftp ganglia-client ganglia-master git grafana gre http https imap imaps ipp ipp-client ipsec irc ircs iscsi-target isns jenkins kadmin kdeconnect kerberos kibana klogin kpasswd kprop kshell ldap ldaps libvirt libvirt-tls lightning-network llmnr managesieve matrix mdns memcache minidlna mongodb mosh mountd mqtt mqtt-tls ms-wbt mssql murmur mysql nfs nfs3 nmea-0183 nrpe ntp nut openvpn ovirt-imageio ovirt-storageconsole ovirt-vmconsole plex pmcd pmproxy pmwebapi pmwebapis pop3 pop3s postgresql privoxy prometheus proxy-dhcp ptp pulseaudio puppetmaster quassel radius rdp redis redis-sentinel rpc-bind rsh rsyncd rtsp salt-master samba samba-client samba-dc sane sip sips slp smtp smtp-submission smtps snmp snmptrap spideroak-lansync spotify-sync squid ssdp ssh steam-streaming svdrp svn syncthing syncthing-gui synergy syslog syslog-tls telnet tentacle tftp tftp-client tile38 tinc tor-socks transmission-client upnp-client vdsm vnc-server wbem-http wbem-https wsman wsmans xdmcp xmpp-bosh xmpp-client xmpp-local xmpp-server zabbix-agent zabbix-server

I was searching to see if dns was available, so I split the string with tr, then searced with grep:

# firewall-cmd --get-services | tr " " "\n" | grep dns

To get details, use the firewall-cmd --info-service=servicename like this:

# firewall-cmd --get-services | tr " " "\n" | grep dns | xargs -I [] sh -c "firewall-cmd --info-service=[]"
  ports: 53/tcp 53/udp
  ports: 853/tcp
  ports: 5353/udp
  destination: ipv4: ipv6:ff02::fb

So for named (bind), I need the dns service to be enabled:

# firewall-cmd --zone=public --add-service=dns --permanent

Now a –list-services will not show dns as we changed the --permanent configuration, not the current configuration:

# firewall-cmd --list-services
dhcpv6-client ssh

So you need to --reload the --permanent settings:

# firewall-cmd --list-services --permanent
dhcpv6-client dns ssh
# firewall-cmd --reload
# firewall-cmd --list-services
dhcpv6-client dns ssh


Posted in *nix, *nix-tools, bash, bash, Development, iptables, Linux, openSuSE, Power User, Scripting, Software Development, SuSE Linux, Tumbleweed, xargs | Leave a Comment »

linux – How can I find all hardlinked files on a filesystem? – Super User

Posted by jpluimers on 2021/08/25

[WayBack] linux – How can I find all hardlinked files on a filesystem? – Super User

use the following line (for sure you have to replace /PATH/FOR/SEARCH/ with whatever you want to search):

find /PATH/FOR/SEARCH/ -xdev -printf '%i\t%n\t%p\n' | fgrep -f <(find . -xdev -printf '%i\n' | sort -n | uniq -d) | sort -n

this scans the filesystem only once, shows inode, number of hardlinks and path of files with more than one hardlink and sorts them according to the inode.

if you are annoyed by error messages for folders you aren’t allowed to read, you can expand the line to this:

find /PATH/FOR/SEARCH/ -xdev -printf '%i\t%n\t%p\n' 2> /dev/null | fgrep -f <(find . -xdev -printf '%i\n' 2> /dev/null | sort -n | uniq -d) | sort -n

It uses these commands:


Posted in *nix, *nix-tools, bash, bash, Development, fgrep, find, Power User, Scripting, Software Development | 1 Comment »

bash – Search for a previous command with the prefix I just typed – Unix & Linux Stack Exchange

Posted by jpluimers on 2021/08/18

[WayBack] bash – Search for a previous command with the prefix I just typed – Unix & Linux Stack Exchange answered by [WayBack] John1024:

What you are looking for is Ctrl-R.

Type Ctrl-R and then type part of the command you want. Bash will display the first matching command. Keep typing CtrlR and bash will cycle through previous matching commands.

To search backwards in the history, type Ctrl-S instead. (If Ctrl-S doesn’t work that way for you, that likely means that you need to disable XON/XOFF flow control: to do that, run stty -ixon.)

This is documented under “Searching” in man bash.

Comment by [WayBack] HongboZhu:

Ctrl-Q to quit the frozen state, if you already hit Ctrl-S without turning off flow control first and got your terminal frozen.

A far more elaborate answer with many other tips is from [WayBack] Peter Cordes:

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, bash, Development, Power User, Scripting, Software Development | Leave a Comment »

UUOC apparently is/was a thing: useless use of cat

Posted by jpluimers on 2021/08/16

A while ago I bumped into UUOC: [WayBack] cat (Unix): Useless use of cat – Wikipedia.

For me the post important reason to choose between cat and a redirect is realising from the above article:

  • input redirection forms allow command to perform random access on the file, whereas the cat examples do not.
  • cat written with UUOC might still be preferred for readability reasons, as reading a piped stream left-to-right might be easier to conceptualize

I ended up at UUOC through [WayBack] bash – Calling multiple commands through xargs – Stack Overflow.

Invoking multiple commands with the same xargs parameter.

The above question also led me to two better solutions for my original xargs problem.

I liked both below solutions.

The first (by [WayBack] ckhan) uses sh as subshell and substitutes the parameter with a readable name.

The second (by [WayBack] shivams) uses a function which gets way more readable code when the command-line gets longer.

[WayBack] shell – xargs : using same argument in multiple commands – Unix & Linux Stack Exchange:

  1. you’ll want to explicitly execute a subshell:
    echo 95 | xargs -n1 -I_percent -- sh -c '[ _percent -ge 95 ] && echo "No Space on disk _percent% full -- remove old backups please"'

    Note also I’m using _percent instead of {} to avoid extra quoting headaches with the shell. It’s not a shell variable; still just an xargs replacement string.

  2. An alternative way, which is more readable, is to define a separate function which contains all your other commands and then call that function with xargs in a sub-shell.Hence, for example:
      [ "$1" -ge 95 ] && echo "No Space on disk $1% full -- remove old backups please"
      echo "Another command echoing $1"
    export -f myfunc
    echo 95 | xargs -n1 -I_percent -- sh -c 'myfunc "_percent"'


Posted in bash, Development, Scripting, Software Development | Leave a Comment »

Listing information on all active interfaces on MacOS part 1: getting the active interface names

Posted by jpluimers on 2021/07/29

Listing Listing information on all active interfaces on MacOS is a process involving multiple pieces, which then can be combined together.

Listing all active interfaces try 1

This involves both the -l (list with optional criteria) and -u parameter (the up criterion) as per excerpts from the [] ifconfig(8) [osx man page] / [WayBack] ifconfig Man Page – macOS –

     ifconfig -- configure network interface parameters

     ifconfig -l [-d] [-u] [address_family]

     The ifconfig utility is used to assign an address to a network interface and/or configure network interface parameters.

     The following options are available:


             Specify the address family which affects interpretation of the remaining parameters.  Since an interface can receive transmissions
             in differing protocols with different naming schemes, specifying the address family is recommended.  The address or protocol fami-
             lies currently supported are ``inet'', ``inet6'', and ``link''.  The default is ``inet''.  ``ether'' and ``lladdr'' are synonyms
             for ``link''.


     The -l flag may be used to list all available interfaces on the system, with no other additional information.  Use of this flag is mutually
     exclusive with all other flags and commands, except for -d (only list interfaces that are down) and -u (only list interfaces that are up).


ifconfig -l -u

Each interface on one line:

ifconfig -l -u | xargs -n1 echo

The problem is that on my system, it also lists bridges as active, whereas they are not:

# ifconfig -l -u | xargs -n1 echo

# ifconfig bridge0
    ether 6a:00:02:9a:23:f0 
        id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
        maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
        root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
        ipfilter disabled flags 0x2
    member: en1 flags=3<LEARNING,DISCOVER>
            ifmaxaddr 0 port 5 priority 0 path cost 0
    member: en2 flags=3<LEARNING,DISCOVER>
            ifmaxaddr 0 port 6 priority 0 path cost 0
    Address cache:
    nd6 options=201<PERFORMNUD,DAD>
    status: inactive

So this is where the MacOS and BSD documentation is inaccurate.

Interface types

The above interfaces are many more than just ethernet or WiFi interfaces; there is a list at [WayBack] macos – What are en0, en1, p2p, and so on, that are displayed after executing ifconfig? – Stack Overflow by [WayBackmcint:

In arbitrary order of my familarity / widespread relevance:

lo0 is loopback.

en0 at one point “ethernet”, now is WiFi (and I have no idea what extra en1 or en2 are used for).

fw0 is the FireWire network interface.

stf0 is an IPv6 to IPv4 tunnel interface to support the transition from IPv4 to the IPv6 standard.

gif0 is a more generic tunneling interface [46]-to-[46].

awdl0 is Apple Wireless Direct Link

p2p0 is related to AWDL features. Either as an old version, or virtual interface with different semantics than awdl.

many VPNs will add additional devices, often “utun#” or “utap#” following TUN/TAP (L3/L2)virtual networking devices.

More on AWDL at [WayBack] ios – What is AWDL (Apple Wireless Direct Link) and how does it work? – Stack Overflow.

Listing all active interfaces try 2

Read the rest of this entry »

Posted in *nix, *nix-tools, Apple, bash, Development, ifconfig, Mac OS X / OS X / MacOS, Power User, Scripting, Software Development | Leave a Comment »

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