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If you need to
rip a CD
from a command-line interface (CLI) on a
CentOS Linux
system,
cdparanoia will allow you to do so. The cdparanoia
CD ripper
program will allow you to produce Waveform Audio File Format, i.e., .WAV, files
from the tracks on a CD. You can use the
yum package management software to install the software
with by issuing the command yum install cdparanoia from the
root account.
[ More Info ]
Sometimes you may find that a software package that you would like to use on a CentOS Linux system is unavailable from the default software repositories, aka "repos." In such cases adding alternative repos, such as Extra Packages for Enterprise Linux (EPEL) or RPM Fusion may allow you to locate the desired package. E.g., the VLC media player is available in the RPM Fusion repository, but not the default ones nor in EPEL. RPM Fusion has two separate software repositories, one that contains free and open-source software (FOSS) and another named "nonfree". Packages in the "nonfree" repository still won't cost you anything, but there may be restrictions on the use of the software, e.g., you may be forbidden from using the software for commercial use. The RPM Fusion site defines the nonfree repo as being 'for redistributable software that is not Open Source Software (as defined by the Fedora Licensing Guidelines); this includes software with publicly available source-code that has "no commercial use"-like restrictions.'
[ More Info ]
If you wish to check the speed of network interfaces on a CentOS Linux system, if the nm-tool utility, is installed, then you can use it to determine the speed of the network ports.
$ nm-tool
NetworkManager Tool
State: disconnected
- Device: em1 ------------------------------------------------------------------
Type: Wired
Driver: bnx2
State: unmanaged
Default: no
HW Address: D4:AE:52:CD:0A:D4
Capabilities:
Carrier Detect: yes
Speed: 1000 Mb/s
Wired Properties
Carrier: on
- Device: em2 ------------------------------------------------------------------
Type: Wired
Driver: bnx2
State: unmanaged
Default: no
HW Address: D4:AE:52:CD:0A:D5
Capabilities:
Carrier Detect: yes
Wired Properties
Carrier: off
$If it is installed, the nm-tool program will likely be in /usr/bin
. It is part of the NetworkManager package.
[ More Info ]
If you are logged into a CentOS Linux system, there are a few ways you can determine the version of CentOS running on the system from a command-line interface (CLI), i.e., a shell prompt.
In the /etc directory, there should be a
/etc/centos-release file containing information on the version
of CentOS.
$ ls -l /etc/*elease -rw-r--r-- 1 root root 27 Mar 28 2017 /etc/centos-release -rw-r--r--. 1 root root 152 Nov 25 2013 /etc/lsb-release lrwxrwxrwx 1 root root 14 Apr 20 2017 /etc/redhat-release -> centos-release lrwxrwxrwx 1 root root 14 Apr 20 2017 /etc/system-release -> centos-release $ cat /etc/*elease CentOS release 6.9 (Final) LSB_VERSION=base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphi cs-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch CentOS release 6.9 (Final) CentOS release 6.9 (Final) $
To just see the version number, you can use one of the grep commands below.
$ grep -oE '[0-9]+\.[0-9]+' /etc/redhat-release 6.9 $ grep -oE '[0-9]+\.[0-9]+' /etc/centos-release 6.9 $
[ More Info ]
If you need to burn a CD or DVD from an
ISO file
from the command line on a Linux system, you can use the
cdrecord
command. If you include the -v argument to the program, you will
see verbose information on the actions performed by the utility and the
progress as it writes to the optical disc. When the program is finished
you can use the eject
command to eject the disc.
[ More Info ]
I needed to remove an IP address from the "jail" it was placed in by fail2ban, which is intrusion prevention sotware, due to an incorrect password being entered too many times by a legitimate user of the system during attempts to log into a CentOS Linux system that runs fail2ban. The attempted logins were made via Secure Shell (SSH). After the number of attempts with an incorrect password reached the cutoff for fail2ban to automatically ban the IP address from which the login attempts were originating, the user then got the following error message on subsequent login attempts:
$ ssh jdoe@example.com ssh: connect to host example.com port 22: Connection refused $
The fail2ban log on the system is at /var/log/fail2ban.log.
You can check that log to see which IP addresses were banned and the time any
bans went into effect. So I first verified the IP address from which
the login attempts were made.
# tail -n 3 /var/log/fail2ban.log 2017-07-13 21:59:06,304 fail2ban.filter [1664]: INFO [sshd] Found 192.168.1.21 2017-07-13 21:59:06,818 fail2ban.actions [1664]: NOTICE [sshd] Ban 192.168.1.21 2017-07-13 21:59:11,538 fail2ban.filter [1664]: INFO [sshd] Found 192.168.1.21 #
You can determine the name for the jail and IP address is in by issuing
the command fail2ban-client status.
[ More Info ]
If you need to know the model number and/or serial number of a hard disk drive (HDD) in a Linux system, one tool that you can use to obtain that information as well as other information on the drive is the lsblk utility, which is included in the util-linux package. E.g.:
# lsblk -o MODEL,SERIAL,SIZE,STATE --nodeps MODEL SERIAL SIZE STATE WDC WD10EZEX-00W WD-WCC6Y4ZYE4Y3 931.5G running DVD A DH16ACSHR 238229911623 1024M running vmDisk-CD 13043003455 1024M running
You can see the list of arguments you can provide to the program with
lsblk -h.
[ More Info ]
On a Linux
system, you can use the lscpu command to obtain information on the system's
Central Processing Unit (CPU). On a
CentOS Linux
system, the utility is included in the util-linux package. On a CentOS system,
you can install that package using the
yum
package management utility, if it isn't already installed, using
yum install util-linux. You can check on whether the
lscpu program is already present using which lscpu and, on
a CentOS system or another system that uses
RPM,
you can use rpm -qi util-linux to determine if the util-linux
package is already installed.
[ More Info ]
If you wish to monitor the top bandwidth consuming processes on a Linux system, you can use the nethogs program, which displays bandwidth usage by process. It will display the process id (PID) of the processes consuming the most bandwidth. E.g.:
NetHogs version 0.8.5 PID USER PROGRAM DEV SENT RECEIVED 19355 jim sshd: jim@pts/0 enp1s4 0.188 0.082 KB/sec 15022 apache /usr/sbin/httpd enp1s4 0.000 0.000 KB/sec ? root unknown TCP 0.000 0.000 KB/sec TOTAL 0.188 0.082 KB/sec
The above output shows me that the two processes consuming the most bandwidth at the time the program was run had PIDs of 19355 and 15022. I can get additional information on those processes using the ps command.
$ ps 19355 PID TTY STAT TIME COMMAND 19355 ? S 0:19 sshd: jim@pts/0 $ ps 15022 PID TTY STAT TIME COMMAND 15022 ? S 0:00 /usr/sbin/httpd -DFOREGROUND $
[ More Info ]
Sometimes network performance problems on a system can be due to a mismatch
in the speed and/or
duplex settings on a system and the switch or router to which it connects.
Autonegotiation normally works to ensure that two connected devices have
compatible settings, but occasionally it may not work as intended. On a Linux
system, one way to check the spped and duplex values is by using the
ethtool command. If the
utility, which provides capabilities for querying and changing settings such
as speed, port, auto-negotiation, PCI locations and checksum offload on many
network devices, especially of Ethernet devices, isn't installed already
you can install it on a
Ubuntu Linux system with the command sudo
apt-get install ethtool. On a
CentOS Linux
system, you can use yum install ethtool. You can run the software
to show the settings for a
network
interface controller (NIC) by issuing the command ethtool devname
where devname is the name associated with the
network interface, e.g., you might issue the command
ethtool eth0 on a Ubuntu system. You can see the available network
interfaces using the command ifconfig -a. Below is the output of
the command run on a CentOS system:
$ ethtool enp1s4 Settings for enp1s4: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: 100Mb/s Duplex: Full Port: Twisted Pair PHYAD: 0 Transceiver: internal Auto-negotiation: on MDI-X: Unknown Cannot get wake-on-lan settings: Operation not permitted Current message level: 0x00000037 (55) drv probe link ifdown ifup Link detected: yes $
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