Chris Pedro

Just a guy from Bermuda

Useful Linux Commands

Last Updated: 2019-05-08

Below is just a random dump of useful commands I use frequently, in no particular order.

In case you’re unfamiliar with the syntax, if you see $ it means you can run the command as an unprivileged user, # needs to be run as root.

Run Local HTTP Server Using Python

This is usable on any machine running Python. Useful for copying new OS images to a Cisco or VyOS router from a laptop or something else, without running a full blow webserver. There’s different commands based on which version of python you’re running.

Python 3:

$ python -m http.server 8000

Python 2:

$ python -m SimpleHTTPServer 8000

Zero out the MBR on a disk

Useful if you quickly want to re-install an OS from PXE or CD, but don’t want to muck around with changing the BIOS boot order. Data will still be on the disk, but it just blows away the MBR. Change /dev/sda to your boot disk.

$ sudo dd if=/dev/zero of=/dev/sda count=1 bs=512

Hard-code Interface Speed and Duplex

This comes in handy when connecting to some network devices that don’t like to properly auto-negotiate. If you’re seeing you interface coming up at half-duplex, you can force the network to a certain setting.

$ sudo ethtool -s <int> speed <speed> duplex full autoneg off

To re-enable auto-negotiation:

$ sudo ethtool -s <int> autoneg on

To see current settings and state:

$ sudo ethtool <int>

$ sudo ethtool enp0s20f3
Settings for enp0s20f3:
	Supported ports: [ TP ]
	Supported link modes:   10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Full
	Supported pause frame use: Symmetric
	Supports auto-negotiation: Yes
	Advertised link modes:  10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Full
	Advertised pause frame use: Symmetric
	Advertised auto-negotiation: Yes
	Speed: 100Mb/s
	Duplex: Half
	Port: Twisted Pair
	PHYAD: 3
	Transceiver: internal
	Auto-negotiation: on
	MDI-X: off (auto)
	Supports Wake-on: pumbg
	Wake-on: g
	Current message level: 0x00000007 (7)
			       drv probe link
	Link detected: yes
$ sudo ethtool -s enp0s20f3 speed 100 duplex full autoneg off
$ sudo ethtool enp0s20f3
Settings for enp0s20f3:
	Supported ports: [ TP ]
	Supported link modes:   10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Full
	Supported pause frame use: Symmetric
	Supports auto-negotiation: Yes
	Advertised link modes:  Not reported
	Advertised pause frame use: Symmetric
	Advertised auto-negotiation: No
	Speed: 100Mb/s
	Duplex: Full
	Port: Twisted Pair
	PHYAD: 3
	Transceiver: internal
	Auto-negotiation: off
	MDI-X: off (auto)
	Supports Wake-on: pumbg
	Wake-on: g
	Current message level: 0x00000007 (7)
			       drv probe link
	Link detected: yes

Show Interface Error Counts

Show the RX and TX errors on an interface in a nice readable format. Change <int> to be whatever interface you want to see stats for. Adapted from here.

# for i in /sys/class/net/<int>/statistics/*; do echo -n "${i##*/}: "; cat $i; done
collisions: 0
multicast: 0
rx_bytes: 0
rx_compressed: 0
rx_crc_errors: 0
rx_dropped: 0
rx_errors: 0
rx_fifo_errors: 0
rx_frame_errors: 0
rx_length_errors: 0
rx_missed_errors: 0
rx_over_errors: 0
rx_packets: 0
tx_aborted_errors: 0
tx_bytes: 0
tx_carrier_errors: 0
tx_compressed: 0
tx_dropped: 0
tx_errors: 0
tx_fifo_errors: 3
tx_heartbeat_errors: 0
tx_packets: 0
tx_window_errors: 0

Add VLAN Interface

Check if module is loaded. If not, load it:

$ modinfo 8021q
$ modprobe --first-time 8021q

Commands to add VLAN interface, assign IP and up.

$ sudo ip link add link <dev> name vlan<X> type vlan id <X>
$ sudo ip addr add <ip>/<prefix> dev vlan<X>
$ sudo ip link set vlanX up

Add static route

$ sudo ip route add <network>/<prefix> via <gw> dev <dev>

Remount partition as read/write

$ sudo mount -o remount,rw <partition>

Remount partition as read-only

$ sudo mount -o remount,ro <partition>

Identify Ethernet interface by PCI address

I’ve used this multiple times with some boxes that have many interfaces.

First run lscpi to make get the PCI address of all Ethernet interfaces. The PCI address is the first part of the message, eg. “01:00.0”

# lspci | grep Ethernet
02:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
02:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
02:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
02:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
04:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
04:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
04:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
04:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
06:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
06:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
06:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
06:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
08:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
08:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
08:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
08:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0a:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0a:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0a:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0a:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0c:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0c:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0c:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0c:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
0e:00.0 Ethernet controller: Intel Corporation Ethernet Controller X710 for 10GbE SFP+ (rev 02)
0e:00.1 Ethernet controller: Intel Corporation Ethernet Controller X710 for 10GbE SFP+ (rev 02)
0e:00.2 Ethernet controller: Intel Corporation Ethernet Controller X710 for 10GbE SFP+ (rev 02)
0e:00.3 Ethernet controller: Intel Corporation Ethernet Controller X710 for 10GbE SFP+ (rev 02)
11:00.0 Ethernet controller: Intel Corporation I210 Gigabit Network Connection (rev 03)

Next, run dmesg to show the interfaces and their PCI addresses:

# dmesg | grep 'renamed from' | egrep 'igb|i40e' | awk '{print $5, $4}' | sort
enp12s0f0: 0000:0c:00.0
enp12s0f1: 0000:0c:00.1
enp12s0f2: 0000:0c:00.2
enp12s0f3: 0000:0c:00.3
enp14s0f0: 0000:0e:00.0
enp14s0f1: 0000:0e:00.1
enp14s0f2: 0000:0e:00.2
enp14s0f3: 0000:0e:00.3
enp17s0: 0000:11:00.0
enp2s0f0: 0000:02:00.0
enp2s0f1: 0000:02:00.1
enp2s0f2: 0000:02:00.2
enp2s0f3: 0000:02:00.3
enp4s0f0: 0000:04:00.0
enp4s0f1: 0000:04:00.1
enp4s0f2: 0000:04:00.2
enp4s0f3: 0000:04:00.3
enp8s0f0: 0000:08:00.0
enp8s0f1: 0000:08:00.1
enp8s0f2: 0000:08:00.2
enp8s0f3: 0000:08:00.3
ens15f0: 0000:06:00.0
ens15f1: 0000:06:00.1
ens15f2: 0000:06:00.2
ens15f3: 0000:06:00.3
ens1f0: 0000:0a:00.0
ens1f1: 0000:0a:00.1
ens1f2: 0000:0a:00.2
ens1f3: 0000:0a:00.3