https://wiki.bash-hackers.org/


Update PostgreSQL
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wget -q https://www.postgresql.org/media/keys/ACCC4CF8.asc -O - | sudo apt-key add -

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -cs`-pgdg main" >> /etc/apt/sources.list.d/pgdg.list'

sudo apt-get update

sudo apt-get install postgres-10

sudo su - postgres

psql


Set PSQL defaults
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put .psqlrc in home directory
\set x '\\setenv PAGER less'
\set xx '\\setenv PAGER \'pspg -bX --no-mouse\''


Size of directory: `du -hcs //mnt/c/PostgreSQL/cassandra30/`

list lines in file `wc file`


General tasks
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wc - print line counts

free - memory usage

du - disk space by file

Resource Limit
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`ulimit -a` to see all limits
file at /etc/security/limits.conf to configure defaults


MySQL
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connection like `mysql -u root -p`

`show databases;`

user is in the format root@127.0.0.1

`grant all prviileges on *.* to 'root'@'127.0.0.1'`

data is stored in /var/lib/mysql

failure to drop a db can be due to presence of unknown file in the database directory

SSH
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add client
* client uses ssh-keygen to create a key in `/home/un/.ssh/` under files `id_rsa` and `id_rsa.pub`
* host setup //etc/ssh/sshd_config to allow passwords and restart
* client uses `ssh-copy-id host_address -p port_num` to move the key to the host
* client uses `ssh` to login

rename files in the current director
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rename 's/find_this_in_the_file_name/replace_with_this/g' *