# Linux - Bag of Tricks ## Introduction This document has many useful command. ### Linux Set Time Examples You can also simplify format using following syntax: ```shell date +%Y%m%d -s "20081128" ``` To set time use the following syntax: ```shell date +%T -s "10:13:13" ``` Use the following syntax to set new data and time: ```shell date --set="STRING" ``` For example, set new data to 2 Oct 2006 18:00:00, type the following command as root user: ```shell date -s "2 OCT 2006 18:00:00" ``` OR ```shell date --set="2 OCT 2006 18:00:00" ``` ### Rsync Copy Examples This is to move files from one server to another Ending the folder WITHOUT a “/” slash means copy that folder everything in that folder Ending the folder WITH a “/” slash means copy everything within that folder Example for “remote to local” location ```shell rsync -chavzP --stats --progress -e ssh user@remote_host:/remote_folder/dir1/ /local_folder/dir1/ ``` Example for “local to remote” location ```shell rsync -chavzP --stats --progress -e ssh /local_folder/dir1/ user@remote_host:/remote_folder/dir1/ ``` ### Rsync Auto Login while sending Example to add a Rsync key on the remote server On the local server simply login as a given user ex: ROOT or USER ```shell ssh-keygen -t rsa ``` If it already exists simply hit "n"
Generating public/private rsa key pair. Enter file in which to save the key (/root/.ssh/id\_rsa): /root/.ssh/id\_rsa already exists. Overwrite (y/n)?
If not then simply hit enter through all options Example: of using ROOT
Generating public/private rsa key pair. Enter file in which to save the key (/root/.ssh/id\_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /root/.ssh/id\_rsa Your public key has been saved in /root/.ssh/id\_rsa.pub The key fingerprint is: SHA256:JoMN/cxvsqZWBHws4eyrU5Q0F0qRe//44qdrrjiQmbU root@DSS-US-TMAP-XXX The key's randomart image is: +---\[RSA 3072\]----+ | .+=.. | | =B.+ | | ..=O | | ==+o | | = E=... | | o... oo | | ..o..++ o | | .oo+o==\*. | +----\[SHA256\]-----+ You have mail in /var/spool/mail/root
Run the following to add the key to the remote server, you can also use IP instead of host name ```shell ssh-copy-id -i ~/.ssh/id_rsa.pub remuser@sfl-lin-001 ``` Example of using a USER you will have to enter yes and the USER password
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id\_rsa.pub" The authenticity of host 'sfl-lin-020 (192.168.136.80)' can't be established. ED25519 key fingerprint is SHA256:oZnvrgY+2Xpd2/huaffvzLMBAgI52AMPUmq/LPLIXbE. This key is not known by any other names Are you sure you want to continue connecting (yes/no/\[fingerprint\])? yes /usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed /usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys remuser@dss-us-map-020's password: tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified tput: No value for $TERM and no -T specified Number of key(s) added: 1 Now try logging into the machine, with: "ssh 'remuser@sfl-lin-020'" and check to make sure that only the key(s) you wanted were added.
Optional: If the command cannot be run above you can copy the key to the remote server manually into the “authorized\_keys” file ```shell cd cd .ssh vi authrized_keys ``` Optional: Change the permissions on the local server ```shell chmod 600 ~/.ssh/* chmod 711 ~/.ssh chmod 711 ~ ``` ### Synology Rsync ```shell rsync -aXHmS --syno-acl /volum1/[xxx] /volume2/[xxx] ``` -a, --archive archive mode; equals -rlptgoD (no -H,-A,-X) -p, --perms preserve permissions -X, --xattrs preserve extended attributes -o, --owner preserve owner (super-user only) -g, --group preserve group \--syno-acl copy Synology ACL data I use the following options myself: rsync -avhxWog --stats --backup --suffix $OLDSUFFIX --exclude-from=$RSYEXCL --syno-pseudo-root No idea why I list options "og" since they're implied by -a, but it works... Regards, Arild PS: "rsync --help" lists all available options for rsync ### Find and Replace String with sed There are several versions of sed, with some functional differences between them. macOS uses the BSD version, while most Linux distributions come with GNU sed pre-installed by default. We’ll use the GNU version. The general form of searching and replacing text using sed takes the following form: ```shell sed -i 's/SEARCH_REGEX/REPLACEMENT/g' INPUTFILE ``` Cop - -i - By default, sed writes its output to the standard output. This option tells sed to edit files in place. If an extension is supplied (ex -i.bak), a backup of the original file is created. - s - The substitute command, probably the most used command in sed. - / / / - Delimiter character. It can be any character but usually the slash (/) character is used. - SEARCH\_REGEX - Normal string or a regular expression to search for. - REPLACEMENT - The replacement string. - g - Global replacement flag. By default, sed reads the file line by line and changes only the first occurrence of the SEARCH\_REGEX on a line. When the replacement flag is provided, all occurrences are replaced. - INPUTFILE - The name of the file on which you want to run the command. ### Find and Replace String with sed within vi This is to search and replace a file globally withing vi ```shell :%s/search_string/replacement_string/g ``` ### Kill Users in Linux This is to be used when trying to kill users using the connection, replace the ? with the number of the session. ```shell pkill -KILL -t pts/? ``` ### Create a CERT First, you need to generate the private key and the Certificate Signing Request (CSR). You can do this via the openssl command: ```shell openssl req -nodes -newkey rsa:2048 -keyout privatekey.key -out mail.csr ``` Then, generate a signing request ```shell openssl x509 -req -days 365 -in mail.csr -signkey privatekey.key -out secure.crt ``` Create a localhost cert on the server ```shell openssl req -newkey rsa:2048 -nodes -keyout /etc/pki/tls/private/localhost.key -x509 -days 365 -out /etc/pki/tls/certs/localhost.crt ``` #### Mariadb Log Rotate If log file is large, try if the logrotate logrotate --force /etc/logrotate.d/mariadb #### MySQL Fail to Start If MySQL does not restart, it probably will not as the index of the log files will not be changed
cd /var/lib/mysql mv ib\_logfile0 ib\_logfile0.old mv ib\_logfile1 ib\_logfile1.old systemctl restart mariadb
#### Configure Rsync Useful for system migrations Create a “/etc/rsyncd.conf” containing: \[root\] exclude = /dev /etc/fstab /proc /sys path = / read only = yes list = yes uid = root gid = root Enable and start: systemctl enable rsyncd.service systemctl start rsyncd.service #### Change Run level systemctl set-default multi-user.target To switch from graphical to multi-user: systemctl isolate multi-user.target; #### Change Local settings \# timedatectl set-timezone Europe/London \# localectl set-locale LANG=en\_GB.UTF-8 \# localectl set-keymap uk Temporary change $ loadkeys us #### Configure Alternate Authentication authconfig-tui #### SSD Considerations Change the value of “`issue_discards”` option from 0 to 1 in “`/etc/lvm/lvm.conf”` `#systemctl enable fstrim.timer` Adjust “/etc/fstab” /dev/mapper/xxx /XXX xfs defaults,noatime,discard 0 0 Optionally set /tmp in RAM \# systemctl enable tmp.mount #### Adding a Disk \# parted /dev/sdx mklabel gpt unit s mkpart primary 2048s 100% set 1 lvm on quit \# pvcreate /dev/sdx1 \# vgcreate rl\_ssd /dev/sdx1 \# lvcreate –L 50GB -n mysql rl\_ssd \# mkfs.xfs /dev/rl-ssd/mysql \# blkid /dev/sdc \# chown mysql:mysql /var/lib/mysql #### Growing a lvm partition \# parted /dev/sdc (parted) unit b (parted) print free Number Start End Size Type File system Flags 1 31744B 5368709119B 5368677376B primary 5368709120B 21474836479B 16106127360B Free Space (parted) resizepart 1 21474836479B (parted) quit \# pvresize /dev/sdc1 ** ** #### **Updating Bootloader configuration** /etc/default/grub grub2-mkconfig -o /boot/grub2/grub.cfg NMAP Scan for all Open Ports TCP ```shell sudo nmap -sT -p- onling.com ``` UDP ```shell sudo nmap -sU -p- onling.com ```