Category: Linux

  • varnish

    How to change varnish port in Ubuntu

    To clear cache, run

    /usr/bin/varnishadm -S /etc/varnish/secret  -T 127.0.0.1:6082 "ban req.http.host ~ .*"

    Get stats

    varnishstat

    See Varnish logs

    varnishlog

    To view logs for “Error 503 Service Unavailable” error.

    varnishlog -q 'RespStatus == 503' -g request

    mod_rpaf help with showing users real IP when site is behind a proxy or varnish.

  • proxy

    debugging proxy

  • install sysstat on centos

    To install sysstat/sar on CentOS, run

    yum install sysstat

    Enable and start sysstat

    systemctl enable sysstat
systemctl start sysstat
systemctl status sysstat

    Allow several minutes to collect data, then you will be able to see stats with sar ommand.

    See sar

  • hdd

    hdd

    blkid
    Checking NVMe Disk
    No space left on device
    smartctl
    sfdisk
    Setup ZFS file system in Ubuntu
    Resize Amazon EC2 Boot Disk
    Partitioning hard disk for backup
    Resize a linux file system with resize2fs
    blkid – show UUID for disks.
    Delayed block allocation failed for inode
    Resize EC2 file system with LVM

    File Systems

    Linux Software Raid

    Disk Errors

  • No space left on device

    On a server, when creating new files, i get error – “No space left on device”.

    root@sok:~# touch 2
touch: cannot touch `2': No space left on device
root@sok:~#

    Check disk space with df -h, it shows 129 GB disk space is free

    root@sok:~# df -h
Filesystem                                              Size  Used Avail Use% Mounted on
rootfs                                                  383G  243G  129G  66% /
udev                                                     10M     0   10M   0% /dev
tmpfs                                                   1.6G  224K  1.6G   1% /run
tmpfs                                                   5.0M     0  5.0M   0% /run/lock
tmpfs                                                   3.5G     0  3.5G   0% /run/shm
tmpfs                                                   3.5G  4.0K  3.5G   1% /tmp
root@sok:~#

    This can be due to inodes getting full, check inodes usage with “df -i”.

    root@sok:~# df -i
Filesystem                                               Inodes    IUsed   IFree IUse% Mounted on
rootfs                                                 25419184 25419184       0  100% /
udev                                                    2057538      319 2057219    1% /dev
tmpfs                                                   2059026      258 2058768    1% /run
tmpfs                                                   2059026        3 2059023    1% /run/lock
tmpfs                                                   2059026        2 2059024    1% /run/shm
tmpfs                                                   2059026        7 2059019    1% /tmp
root@sok:~#

    As you can use Inodes are all used up.

    To find where inodes are used up, run

    find / -xdev -printf '%h\n' | sort | uniq -c | sort -k 1 -n

    If you have recent version of du, you can use

    du --inodes -xS | sort -n

    This will display all folders with inode usage, sorted by inode usage.

  • Disable IPv6

    To disable IPv6, edit

    vi /etc/sysctl.conf

    Add following

    net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

    run

    sysctl -p

    IPv6 config for RHEL

    BOOTPROTO=dhcp
DEFROUTE=yes
DEVICE=eth0
DHCLIENT_SET_DEFAULT_ROUTE=yes
HWADDR=fa:16:3e:83:96:4e
IPV6ADDR=2607:5300:405:300::16dc/56
IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6_DEFAULTGW=2607:5300:405:300::1
IPV6_FORCE_ACCEPT_RA=no
MTU=1500
ONBOOT=yes
TYPE=Ethernet
USERCTL=no

    Related Posts

  • vim E509: Cannot create backup file (add ! to override)

    When i save file on a server in vim, i get error

    “FILE_NAME.EXTN” E509: Cannot create backup file (add ! to override)
    Press ENTER or type command to continue

    I verified vim backupdir with command

    :verbose set backupdir

    That showed “backupdir=.,~/tmp,~/”, i compared it with vim installed on my PC, it looked same.

    I tried to create a file on the server using touch, it failed.

    root@v22013111876215233:/home/firsthost/public_html/themes/blue/styles# touch 2
touch: cannot touch `2': No space left on device
root@v22013111876215233:/home/firsthost/public_html/themes/blue/styles#

    The error was due to disk full on the server and vim was not able to create a backup file.

    See vim

  • vim

    Vim 8 goes Visual Mode on right click
    vim E509: Cannot create backup file (add ! to override)
    Install vim from source on CentOS

    Using vim

  • Vim 8 goes Visual Mode on right click

    Vim 8 shipped with Fedora 25 and Debian 9 when you mouse right click or use middle button to insert text to vim editor, it just go VISUAL mode.

    This is because default changes in Vim 8.

    Solution 1

    The solution is to press SHIFT key before using mouse.

    SHIFT + right mouse button = you will get paste option for copied text.

    SHIFT + middle mouse button (press mouse wheel) = selected text will be pasted to vim.

    SHIFT + INSERT = paste.

    Solution 2

    use vim.tiny, this can be activated by running

    update-alternatives --config vi

    Example

    root@debug-instance:~# update-alternatives --config vi
There are 3 choices for the alternative vi (providing /usr/bin/vi).

  Selection    Path                Priority   Status
------------------------------------------------------------
* 0            /usr/bin/nvim        30        auto mode
  1            /usr/bin/nvim        30        manual mode
  2            /usr/bin/vim.basic   30        manual mode
  3            /usr/bin/vim.tiny    15        manual mode

Press  to keep the current choice[*], or type selection number: 3
update-alternatives: using /usr/bin/vim.tiny to provide /usr/bin/vi (vi) in manual mode
root@debug-instance:~#

    Solution 3

    Run command

    :set mouse-=a

    to make this permanent, edit ~/.vimrc file, add

    set mouse-=a

    See vi

  • apt error after MariaDB to MySQL change

    I have install MariaDB on a Ubuntu 16.04 server. Then installed Virtualmin, that require MySQL, so it removed MariaDB and installed MySQL, this caused apt stop working.

    When i run “apt update”, it failed with

    root@ok-vm:~# apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
 mysql-server : Depends: mysql-server-5.7 but it is not installed
E: Unmet dependencies. Try using -f.
root@ok-vm:~#

    Next i run ‘apt-get -f install’ as it said in above error message.

    root@ok-vm:~# apt-get -f install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Correcting dependencies... Done
The following additional packages will be installed:
  mysql-server-5.7
Suggested packages:
  mailx tinyca
The following NEW packages will be installed:
  mysql-server-5.7
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
167 not fully installed or removed.
Need to get 0 B/2,708 kB of archives.
After this operation, 48.3 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Preconfiguring packages ...
(Reading database ... 120876 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.7_5.7.20-0ubuntu0.16.04.1_amd64.deb ...
Aborting downgrade from (at least) 10.0 to 5.7.
If are sure you want to downgrade to 5.7, remove the file
/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.7_5.7.20-0ubuntu0.16.04.1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
Errors were encountered while processing:
 /var/cache/apt/archives/mysql-server-5.7_5.7.20-0ubuntu0.16.04.1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
root@ok-vm:~#

    That too failed. The error message is

    Preparing to unpack …/mysql-server-5.7_5.7.20-0ubuntu0.16.04.1_amd64.deb …
    Aborting downgrade from (at least) 10.0 to 5.7.

    This is because MySQL detected MairaDB data files in /var/lib/mysql folder, it can’t use same data files as MariaDB is newer version.

    To fix the problem, i renamed the folder

    mv /var/lib/mysql /var/lib/mysql-old

    Now running “apt-get -f install” fixed the problem with apt.

    apt-get -f install

  • apt show

    apt show command shows information about a package.

    root@ok-vm:~# apt show apache2
Package: apache2
Version: 2.4.18-2ubuntu3.5
Priority: optional
Section: web
Origin: Ubuntu
Maintainer: Ubuntu Developers 
Original-Maintainer: Debian Apache Maintainers 
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 501 kB
Provides: httpd, httpd-cgi
Pre-Depends: dpkg (>= 1.17.14)
Depends: lsb-base, procps, perl, mime-support, apache2-bin (= 2.4.18-2ubuntu3.5), apache2-utils (>= 2.4), apache2-data (= 2.4.18-2ubuntu3.5)
Recommends: ssl-cert
Suggests: www-browser, apache2-doc, apache2-suexec-pristine | apache2-suexec-custom, ufw
Conflicts: apache2.2-bin, apache2.2-common
Replaces: apache2.2-bin, apache2.2-common
Homepage: http://httpd.apache.org/
Task: lamp-server, mythbuntu-frontend, mythbuntu-desktop, mythbuntu-backend-slave, mythbuntu-backend-master, mythbuntu-backend-master
Supported: 5y
Download-Size: 86.7 kB
APT-Manual-Installed: yes
APT-Sources: http://azure.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
Description: Apache HTTP Server
 The Apache HTTP Server Project's goal is to build a secure, efficient and
 extensible HTTP server as standards-compliant open source software. The
 result has long been the number one web server on the Internet.
 .
 Installing this package results in a full installation, including the
 configuration files, init scripts and support scripts.

N: There is 1 additional record. Please use the '-a' switch to see it
root@ok-vm:~#

    See apt policy apt

  • apt policy

    apt policy command show information about a package.

    root@ok-vm:~# apt policy  apache2
apache2:
  Installed: 2.4.18-2ubuntu3.5
  Candidate: 2.4.18-2ubuntu3.5
  Version table:
 *** 2.4.18-2ubuntu3.5 500
        500 http://azure.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.4.18-2ubuntu3 500
        500 http://azure.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
root@ok-vm:~#

    It shows the installed version “Installed: 2.4.18-2ubuntu3.5” and the repo from where it is installed.

    See apt