Centos 7 reset root/ any user lost password / lockout due to cant remember password

1. Need to be in front of the terminal. (Physically if not vm).

2. Reboot the server

3. Press 'e' in the GRUB2 boot screen.

3. bunch of text will come out. We can edit those text. 

• find the line that load the kernel - begins with 'linux16' in my case.
• find text "rhgb quiet" , replace it with "rd.break enforcing=0".
• When done. Press Ctrl X. The system will boot with the parameter edited.

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4. after boot. terminal prompt appear.

• remount the root filesystem. "# mount -o remount,rw /sysroot"
• set the environment to /sysroot "# chroot /sysroot/"
• change desired password. root/any other user. "# passwd root"
• when done. remount / to readonly back "# mount -o remount, ro /"
• Then "# exit". 
• Then "# exit" again. system continue to boot.
• login as root with the newly created password. DO NOT REBOOT YET.
• SELinux will detect that the password file /etc/shadow has been changed and will restrict access to it).  Instead, you must first restore the SELinux labels on that file:
  
• "# restorecon /etc/shadow".
• Then reboot

reference: https://www.datacentreplus.co.uk/support/knowledge-base/reset-root-password-in-centos-7/

mysql_upgrade return error "Can't get stat of './mysql/general_log.CSV"

mysql_upgrade return error

Phase 3/6: Running 'mysql_fix_privilege_tables'
ERROR 13 (HY000) at line 286: Can't get stat of './mysql/general_log.CSV' (Errcode: 2 "No such file or directory")
ERROR 13 (HY000) at line 297: Can't get stat of './mysql/slow_log.CSV' (Errcode: 2 "No such file or directory")
ERROR 13 (HY000) at line 299: Can't get stat of './mysql/slow_log.CSV' (Errcode: 2 "No such file or directory")
ERROR 13 (HY000) at line 301: Can't get stat of './mysql/slow_log.CSV' (Errcode: 2 "No such file or directory")
FATAL ERROR: Upgrade failed

Solution:

Permalink

Elena Stepanova added a comment - 2016-10-11 17:42

This is very strange that general_log.CSV and slow_log.CSV did not exist, do you know how it happened? Did somebody remove them manually?
Did general_log.frm and slow_log.frm files exist?
The most likely reason for the problem is that due to the disappearance of CSV files, the tables were left in an inconsistent state.
You can try to do the following:

# Make sure there are no remains of the table

- rm ./mysql/general_log.* ./mysql/slow_log.*

# connect to the server and run

[MariaDB]> FLUSH TABLES;

# Then re-run

mysql_upgrade -uroot -p --force

It should work unless somebody previously tried to convert general_log and slow_log tables into InnoDB, in this case things can be a bit more complicated.

source: https://jira.mariadb.org/browse/MDEV-11032

Apache get concurrent connection

Reference: https://www.cloudtechtiq.com/blog/check-apache-concurrent-connections-using-netstat-command

To Count Apache concurrent connection's, use any of the below commands.

netstat -nt | grep :80 | wc -l    

netstat -plan|grep :80 | wc -l    

netstat -an | grep 'EST' | wc -l    

netstat -ant | grep ESTABLISHED | grep :80 | wc -l    

ps -A | grep httpd | wc -l    

ps -ef | grep http | wc -l    

ps aux | grep httpd | wc -l    

ps aux | grep http | grep -v "\(root\|grep\)" | wc -l

To print the active Internet connections to the server at port 80 and sort the results, use the below commands.

netstat -an | grep :80 | sort 

netstat -plan | grep :80 

netstat -anp | grep :80

To calculate and count, number of connection currently established from each IP address with server.

netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n

To calculate and count, number of connection currently established from each IP address through TCP or UDP protocol with server.

netstat -anp |grep 'tcp\|udp' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n

To Print ESTABLISHED connections instead of all connections, and displays the connections count for each IP

netstat -ntu | grep ESTAB | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr

To print the list of IP address and its connection count, that connect to port 80 on the server.

netstat -plan|grep :80|awk {'print $5'}|cut -d: -f 1|sort|uniq -c|sort -nk 1

To print all the apache httpd actual processes in Linux, use the below commands.

ps -aux | grep httpd  or  ps -ef | grep httpd

mysqldump comparison using compress option with bzip2 and gzip performance and the output size

[root@server2 vagrant]# time mysqldump --compress myportal | gzip  > test.gz

real 0m14.675s

user 0m7.426s

sys 0m0.618s

[root@server2 vagrant]# time mysqldump  myportal | gzip  > test.gz

real 0m9.455s

user 0m6.343s

sys 0m0.646s

[root@server2 vagrant]# time mysqldump --compress myportal | gzip  > test-compress-gzip.gz

real 0m14.603s

user 0m7.371s

sys 0m0.580s

[root@server2 vagrant]# time mysqldump  myportal | gzip  > test--gzip.gz

real 0m9.357s

user 0m6.314s

sys 0m0.668s

[root@server2 vagrant]# time mysqldump  myportal | bzip2  > test--bzip.bz2

real 1m10.520s

user 1m7.152s

sys 0m0.739s

[root@server2 vagrant]# time mysqldump --compress  myportal | bzip2  > test-compress-bzip.bz2

real 1m15.358s

user 1m7.156s

sys 0m0.773s

[root@server2 vagrant]# du -h test-*

6.7M test--bzip.bz2

13M test--gzip.gz

6.7M test-compress-bzip.bz2

13M test-compress-gzip.gz

[root@server2 vagrant]# du  test-*

6808 test--bzip.bz2

12376 test--gzip.gz

6808 test-compress-bzip.bz2

12376 test-compress-gzip.gz

bzip2 compress more than gzip but the process time is longer than gzip. 

So please choose between speed and compression ratio, which suite ur needs.

Regex to find space

(?:^.+?\K | (?=[0-9]+.+))

Show hidden files and sub directories in root directory

By default the root directory will not show you the directories like /usr, /bin, /etc etc. To make them visible you need to show the hidden files.

Open terminal and type the following command and hit return.

defaults write com.apple.finder AppleShowAllFiles -bool TRUE;killall Finder

Reference: https://themacbeginner.com/view-content-root-directory-mac-os-x/

rescue corrupted mbr centos / linux

https://wiki.centos.org/TipsAndTricks/ReinstallGRUB

Apache ProxyPass Proxy to remain original host ip on request.

source: https://www.leaseweb.com/labs/2014/12/tutorial-apache-2-4-transparent-reverse-proxy/

Mysql On delete cascade reference information

Tips to find tables affected by MySQL ON DELETE CASCADE action

Sometimes, it is useful to know which table is affected by the MySQL ON DELETE CASCADE  referential action when you delete data from a table. You can query this data from the referential_constraints in the information_schema  database as follows:

1 2 3 4 5 6 7 8 9 10

USE information_schema;   SELECT     table_name FROM     referential_constraints WHERE     constraint_schema = 'database_name'         AND referenced_table_name = 'parent_table'         AND delete_rule = 'CASCADE'

source: http://www.mysqltutorial.org/mysql-on-delete-cascade/

mariadb @ mysql change datadir to /home/ directory

chcon -R -u system_u -r object_r -t mysqld_db_t $DATADIR

Troubleshooting “Permission denied” when attempting to connect to Redis from PHP script

Problem solved, type:

/usr/sbin/setsebool httpd_can_network_connect=1

By default, SELinux does not allow Apache to make socket connections. More information can be found here.

source: https://stackoverflow.com/questions/8765848/troubleshooting-permission-denied-when-attempting-to-connect-to-redis-from-php