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Tue, Dec 12, 2017 11:25 pm
NetworkManager and nm-tool
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 ]
[/os/unix/linux/centos]
permanent link
Sun, Dec 10, 2017 7:39 pm
Determining the version of CentOS on a system
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 ]
[/os/unix/linux/centos]
permanent link
Sat, Jul 15, 2017 10:51 pm
Burning a CD/DVD on a Linux system with the cdrecord command
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 ]
[/os/unix/linux/utilities/cd-dvd]
permanent link
Thu, Jul 13, 2017 11:00 pm
Unbanning an IP address banned with fail2ban
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 ]
[/os/unix/linux]
permanent link
Tue, Jul 04, 2017 10:47 pm
Determining the model and serial number of a HDD in a Linux system
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 ]
[/os/unix/linux/utilities/sysmgmt]
permanent link
Fri, Jun 23, 2017 10:22 pm
lscpu
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 ]
[/os/unix/linux/utilities/sysmgmt]
permanent link
Tue, Jun 20, 2017 10:22 pm
NetHogs
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 ]
[/os/unix/linux/network]
permanent link
Tue, May 23, 2017 10:36 pm
Checking speed and duplex settings on a Linux system
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
$
[/os/unix/linux/utilities/network]
permanent link
Tue, Mar 28, 2017 9:39 pm
Determining which packages were recently installed on a CentOS Linux system
I needed to determine which packages were recently installed on a
CentOS
7 system where
yum is used to install packages. The command
rpm -qa --last
will list all packages that have been installed
in chronological order with the most recently installed packages listed
first, since the --last
option orders the package listing by
install time such that the latest packages are at the top. E.g.:
# rpm -qa --last
amarok-utils-2.8.0-19.el7.x86_64 Fri 12 Aug 2016 09:02:34 PM EDT
amarok-libs-2.8.0-19.el7.x86_64 Fri 12 Aug 2016 09:02:34 PM EDT
amarok-2.8.0-19.el7.x86_64 Fri 12 Aug 2016 09:02:31 PM EDT
taglib-extras-1.0.1-8.el7.x86_64 Fri 12 Aug 2016 09:02:17 PM EDT
mariadb-embedded-5.5.50-1.el7_2.x86_64 Fri 12 Aug 2016 09:02:17 PM EDT
qjson-0.8.1-4.el7.x86_64 Fri 12 Aug 2016 09:02:15 PM EDT
kdelibs-webkit-4.14.8-1.el7.x86_64 Fri 12 Aug 2016 09:02:14 PM EDT
qtscriptbindings-0.2.0-5.el7.x86_64 Fri 12 Aug 2016 09:02:13 PM EDT
qtwebkit-2.3.4-6.el7.x86_64 Fri 12 Aug 2016 09:01:57 PM EDT
alpine-2.20-2.el7.x86_64 Mon 08 Aug 2016 10:13:54 PM EDT
fuse-sshfs-2.5-1.el7.x86_64 Mon 08 Aug 2016 09:28:26 PM EDT
gpg-pubkey-352c64e5-52ae6884 Mon 08 Aug 2016 09:27:13 PM EDT
epel-release-7-6.noarch Mon 08 Aug 2016 09:12:51 PM EDT
lynx-2.8.8-0.3.dev15.el7.x86_64 Fri 05 Aug 2016 10:28:17 PM EDT
telnet-0.17-59.el7.x86_64 Sat 30 Jul 2016 04:34:17 PM EDT
thunderbird-45.2-1.el7.centos.x86_64 Sat 30 Jul 2016 04:10:55 PM EDT
mutt-1.5.21-26.el7.x86_64 Sat 30 Jul 2016 03:50:58 PM EDT
<text snipped>
gnu-free-fonts-common-20120503-8.el7.noarch Fri 15 Jul 2016 03:10:39 PM EDT
dejavu-fonts-common-2.33-6.el7.noarch Fri 15 Jul 2016 03:10:39 PM EDT
libgcc-4.8.5-4.el7.x86_64 Fri 15 Jul 2016 03:10:38 PM EDT
fontpackages-filesystem-1.44-8.el7.noarch Fri 15 Jul 2016 03:10:38 PM EDT
control-center-filesystem-3.14.5-8.el7.x86_64 Fri 15 Jul 2016 03:10:38 PM EDT
#
[ More Info ]
[/os/unix/linux/centos]
permanent link
Sun, Mar 26, 2017 5:10 pm
Unrar for Centos 7
I needed to convert a
rar
file to a zip file on a
CentOS 7
Linux system. But when I tried installing an unrar package with
yum, the
package
manager on the system, I found none was available from any of the
software
repositories the system was configured to check for packages.
# yum install unrar
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
* base: centos.firehosted.com
* epel: mirror.us.leaseweb.net
* extras: centos.aol.com
* updates: mirror.umd.edu
No package unrar available.
Error: Nothing to do
# yum install rar
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
* base: centos.firehosted.com
* epel: mirror.us.leaseweb.net
* extras: centos.aol.com
* updates: mirror.umd.edu
No package rar available.
Error: Nothing to do
#
I had previously installed support for the
Extra Packages for
Enterprise Linux (EPEL) repository, but though I thought the unrar package
might be found there, it wasn't found. I did find an
RPM file for the software, howerver, at
RPM CentOS 7 unrar 5.0.12 x86_64 rpm. I downloaded that file with
wget and, since
yum can be used to install RPM files, installed it with yum.
[ More Info ]
[/os/unix/linux/centos/7]
permanent link
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