On a CentOS server, when sending mail from PHP scripts, mail failed to work. On checking postfix log file (/var/log/maillog), i see following error.
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Aug 11 01:41:53 forums postfix/sendmail[44463]: fatal: open /etc/postfix/main.cf: Permission denied |
To fix this, disable selinux
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setenforce 0 |
To permanantly disable SELinux, run
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sed -i 's/SELINUX=enforcing/SELINUX=disabled/' /etc/selinux/config |
[…]
To protect files on Linux by accidently overwritten by > operator, you can use
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set -o noclobber |
Now if you try to overwrite a file with >, you will get error
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root@ok:~# echo "Hello" > 1.txt -bash: 1.txt: cannot overwrite existing file root@ok:~# |
If you really need to overwrite, use >! operator.
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echo "Hello" >! FILE_NAME |
Example
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root@ok:~# echo "Hello" > 1.txt -bash: 1.txt: cannot overwrite existing file root@ok:~# echo "Hello" >! 1.txt root@ok:~# |
Instead of running the command “set -o noclobber” everytime, you can add it […]
On web servers, you may need to get email alert when someone login to your server using SSH. To do this edit file
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vi ~/.bashrc |
Add
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echo "ALERT - Bash shell access by user \"`whoami`\" to server $HOSTNAME on `date` " | mail -s "Alert: Shell access detected from user \"`whoami`\" from IP_Address: `who | cut -d"(" -f2 | cut -d")" -f1`" you@your-domain.com |
In above, replace [email protected] with your actual email address. You need a mail server installed on your server for this to work. If you want to log to a […]
By default VNC Console on a KVM virtual Machine only listens to localhost. So you need to do SSH tunnel to access VNC console. To make VNC available on all interfaces on Host machine, you need to edit file
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vi /etc/libvirt/qemu.conf |
You need to uncomment the line vnc_listen = “0.0.0.0”.
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# VNC is configured to listen on 127.0.0.1 by default. # To make it listen on all public interfaces, uncomment # this next option. # # NB, strong recommendation to enable TLS + x509 certificate # verification when allowing public access # vnc_listen = "0.0.0.0" |
Once this is done, you […]
This script will check disk usage on / partition and email you if disk usage is above 80% We can use df / command to find current disk usage
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df / |
As you can see, the result have 2 lines. We don’t need first line. To ignore first line, we can use
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df / | grep -v 'Filesystem' |
From the result, […]
To install Linux KVM hypervisor on CentOS 8, run
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dnf install qemu-kvm |
Install libvirtd
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dnf install libvirt-daemon libvirt-daemon-kvm libvirt-client |
Enable libvirtd to start on boot
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systemctl enable libvirtd |
Start libvirtd
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systemctl start libvirtd |
To see status, run
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systemctl status libvirtd |
Install virt-install
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dnf install virt-install |
Now you have Linux KVM installed. You can use virt-install or Virt Manager to create virtual machine. See Linux KVM Virtualization […]
I have a movie cut with hjspit.
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-rw-r--r-- 1 root root 110100480 Apr 17 10:42 MSFT_1.avi.001 -rw-r--r-- 1 root root 110100480 Apr 17 10:45 MSFT_1.avi.002 -rw-r--r-- 1 root root 110100480 Apr 17 10:45 MSFT_1.avi.003 -rw-r--r-- 1 root root 110100480 Apr 17 10:47 MSFT_1.avi.004 -rw-r--r-- 1 root root 110100480 Apr 17 10:47 MSFT_1.avi.005 -rw-r--r-- 1 root root 110100480 Apr 17 10:49 MSFT_1.avi.006 -rw-r--r-- 1 root root 110100480 Apr 17 10:49 MSFT_1.avi.007 -rw-r--r-- 1 root root 110100480 Apr 17 10:51 MSFT_1.avi.008 -rw-r--r-- 1 root root 62759034 Apr 17 10:51 MSFT_1.avi.009 |
To join them on Linux, run
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cat MSFT_1.avi.00? > MSFT_1.avi |
[…]
When you run a docker image, it create a container and run it. After docker container stop, container stays, so you can use it again if required. Some times, you need to delete docker container after it is run. This is useful if your docker container is just a command line executable. In my case, […]
One of my internet provider only provide IPv4 connection. When i run apt install command, it failed with error as it try to connect using IPv6.
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boby@sok-01:~$ sudo apt install php7.3-curl Reading package lists... Done Building dependency tree Reading state information... Done The following NEW packages will be installed: php7.3-curl 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 29.6 kB of archives. After this operation, 123 kB of additional disk space will be used. Err:1 http://ppa.launchpad.net/ondrej/php/ubuntu bionic/main amd64 php7.3-curl amd64 7.3.13-1+ubuntu18.04.1+deb.sury.org+1 Could not connect to ppa.launchpad.net:80 (2001:67c:1560:8008::15). - connect (101: Network is unreachable) Could not connect to ppa.launchpad.net:80 (91.189.95.83), connection timed out E: Failed to fetch http://ppa.launchpad.net/ondrej/php/ubuntu/pool/main/p/php7.3/php7.3-curl_7.3.13-1+ubuntu18.04.1+deb.sury.org+1_amd64.deb Could not connect to ppa.launchpad.net:80 (2001:67c:1560:8008::15). - connect (101: Network is unreachable) Could not connect to ppa.launchpad.net:80 (91.189.95.83), connection timed out E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing? boby@sok-01:~$ |
To force apt to use IPv4 only, edit
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sudo vi /etc/apt/apt.conf.d/99-force-ipv4 |
Add
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Acquire::ForceIPv4 "true"; |
If you want to force IPv6, add
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Acquire::ForceIPv6 "true"; |
[…]