# System ## System ### **Work with yum history** ``` # List yum history (e.g install, update) sudo yum history # Example output: # Loaded plugins: extras_suggestions, langpacks, priorities, update-motd # ID | Login user | Date and time | Action(s) | Altered # ------------------------------------------------------------------------------- # 11 | ... | 2020-04-10 10:57 | Install | 1 P< # 10 | ... | 2020-03-27 05:21 | Install | 1 >P # 9 | ... | 2020-03-05 11:57 | I, U | 56 *< # ... # Show more details of a yum history (e.g. history #11) sudo yum history info 11 # Undo a yum history (e.g. history #11, this will uninstall some packages) sudo yum history undo 11 ``` ### **Audit files to see who made changes to a file \[RedHat based system only]** ``` # To audit a directory recursively for changes (e.g. myproject) auditctl -w /path/to/myproject/ -p wa # If you delete a file name "VIPfile", the deletion is recorded in /var/log/audit/audit.log sudo grep VIPfile /var/log/audit/audit.log #type=PATH msg=audit(1581417313.678:113): item=1 name="VIPfile" inode=300115 dev=ca:01 mode=0100664 ouid=1000 ogid=1000 rdev=00:00 nametype=DELETE cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0 ``` ### **Check out whether SELinux is enabled** ``` sestatus # SELinux status: enabled # SELinuxfs mount: /sys/fs/selinux # SELinux root directory: /etc/selinux # Loaded policy name: targeted # Current mode: enforcing # Mode from config file: enforcing # Policy MLS status: enabled # Policy deny_unknown status: allowed # Max kernel policy version: 31 ``` ### **Generate public key from private key** ``` ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub ``` ### **Copy your default public key to remote user** ``` ssh-copy-id @ # then you need to enter the password # and next time you won't need to enter password when ssh to that user ``` ### **Copy default public key to remote user using the required private key (e.g. use your mykey.pem key to copy your id\_rsa.pub to the remote user)** ``` # before you need to use mykey.pem to ssh to remote user. ssh-copy-id -i ~/.ssh/id_rsa.pub -o "IdentityFile ~/Downloads/mykey.pem" @ # now you don't need to use key to ssh to that user. ``` ### **SSH Agent Forwarding** ``` # To bring your key with you when ssh to serverA, then ssh to serverB from serverA using the key. ssh-agent ssh-add /path/to/mykey.pem ssh -A @ # Next you can ssh to serverB ssh @ ``` ### **Set the default user and key for a host when using SSH** ``` # add the following to ~/.ssh/config Host myserver User myuser IdentityFile ~/path/to/mykey.pem # Next, you could run "ssh myserver" instead of "ssh -i ~/path/to/mykey.pem myuser@myserver" ``` ### **Follow the most recent logs from service** ``` journalctl -u -f ``` ### **Eliminate the zombie** ``` # A zombie is already dead, so you cannot kill it. You can eliminate the zombie by killing its parent. # First, find PID of the zombie ps aux| grep 'Z' # Next find the PID of zombie's parent pstree -p -s # Then you can kill its parent and you will notice the zombie is gone. sudo kill 9 ``` ### **Show memory usage** ``` free -c 10 -mhs 1 # print 10 times, at 1 second interval ``` ### **Display CPU and IO statistics for devices and partitions.** ``` # refresh every second iostat -x -t 1 ``` ### **Display bandwidth usage on an network interface (e.g. enp175s0f0)** ``` iftop -i enp175s0f0 ``` ### **Tell how long the system has been running and number of users** ``` uptime ``` ### **Check if it's root running** ``` if [ "$EUID" -ne 0 ]; then echo "Please run this as root" exit 1 fi ``` ### **Change shell of a user (e.g. bonnie)** ``` chsh -s /bin/sh bonnie # /etc/shells: valid login shells ``` ### **Change root / fake root / jail (e.g. change root to newroot)** ``` chroot /home/newroot /bin/bash # To exit chroot exit ``` ### **Display file status (size; access, modify and change time, etc) of a file (e.g. filename.txt)** ``` stat filename.txt ``` ### **Snapshot of the current processes** ``` ps aux ``` ### **Display a tree of processes** ``` pstree ``` ### **Find maximum number of processes** ``` cat /proc/sys/kernel/pid_max ``` ### **Print or control the kernel ring buffer** ``` dmesg ``` ### **Show IP address** ``` $ip add show # or ifconfig ``` ### **Print previous and current SysV runlevel** ``` runlevel # or who -r ``` ### **Change SysV runlevel (e.g. 5)** ``` init 5 #or telinit 5 ``` ### **Display all available services in all runlevels,** ``` chkconfig --list # update-rc.d equivalent to chkconfig in ubuntu ``` ### **Check system version** ``` cat /etc/*-release ``` ### **Linux Programmer's Manuel: hier- description of the filesystem hierarchy** ``` man hier ``` ### **Control the systemd system and service manager** ``` # e.g. check the status of cron service systemctl status cron.service # e.g. stop cron service systemctl stop cron.service ``` ### **List job** ``` jobs -l ``` ### **Run a program with modified priority (e.g. ./test.sh)** ``` # nice value is adjustable from -20 (most favorable) to +19 # the nicer the application, the lower the priority # Default niceness: 10; default priority: 80 nice -10 ./test.sh ``` ### **Export PATH** ``` export PATH=$PATH:~/path/you/want ``` ### **Make file executable** ``` chmod +x filename # you can now ./filename to execute it ``` ### **Print system information** ``` uname -a # Check system hardware-platform (x86-64) uname -i ``` ### **Surf the net** ``` links www.google.com ``` ### **Add user, set passwd** ``` useradd username passwd username ``` ### **Edit PS1 variable for bash (e.g. displaying the whole path)** ``` 1. vi ~/.bash_profile 2. export PS1='\u@\h:\w\$' # $PS1 is a variable that defines the makeup and style of the command prompt # You could use emojis and add timestamp to every prompt using the following value: # export PS1="\t@🦁:\w\$ " 3. source ~/.bash_profile ``` ### **Edit environment setting (e.g. alias)** ``` 1. vi ~/.bash_profile 2. alias pd="pwd" //no more need to type that 'w'! 3. source ~/.bash_profile ``` ### **Print all alias** ``` alias -p ``` ### **Unalias (e.g. after alias ls='ls --color=auto')** ``` unalias ls ``` ### **Set and unset shell options** ``` # print all shell options shopt # to unset (or stop) alias shopt -u expand_aliases # to set (or start) alias shopt -s expand_aliases ``` ### **List environment variables (e.g. PATH)** ``` echo $PATH # list of directories separated by a colon ``` ### **List all environment variables for current user** ``` env ``` ### **Unset environment variable (e.g. unset variable 'MYVAR')** ``` unset MYVAR ``` ### **Show partition format** ``` lsblk ``` ### **Inform the OS of partition table changes** ``` partprobe ``` ### **Soft link program to bin** ``` ln -s /path/to/program /home/usr/bin # must be the whole path to the program ``` ### **Show hexadecimal view of data** ``` hexdump -C filename.class ``` ### **Jump to different node** ``` rsh node_name ``` ### **Check port (active internet connection)** ``` netstat -tulpn ``` ### **Print resolved symbolic links or canonical file names** ``` readlink filename ``` ### **Find out the type of command and where it link to (e.g. python)** ``` type python # python is /usr/bin/python # There are 5 different types, check using the 'type -f' flag # 1. alias (shell alias) # 2. function (shell function, type will also print the function body) # 3. builtin (shell builtin) # 4. file (disk file) # 5. keyword (shell reserved word) # You can also use `which` which python # /usr/bin/python ``` ### **List all functions names** ``` declare -F ``` ### **List total size of a directory** ``` du -hs . # or du -sb ``` ### **Copy directory with permission setting** ``` cp -rp /path/to/directory ``` ### **Store current directory** ``` pushd . # then pop popd #or use dirs to display the list of currently remembered directories. dirs -l ``` ### **Show disk usage** ``` df -h # or du -h #or du -sk /var/log/* |sort -rn |head -10 ``` ### **check the Inode utilization** ``` df -i # Filesystem Inodes IUsed IFree IUse% Mounted on # devtmpfs 492652 304 492348 1% /dev # tmpfs 497233 2 497231 1% /dev/shm # tmpfs 497233 439 496794 1% /run # tmpfs 497233 16 497217 1% /sys/fs/cgroup # /dev/nvme0n1p1 5037976 370882 4667094 8% / # tmpfs 497233 1 497232 1% /run/user/1000 ``` ### **Show all file system type** ``` df -TH ``` ### **Show current runlevel** ``` runlevel ``` ### **Switch runlevel** ``` init 3 #or telinit 3 ``` ### **Permanently modify runlevel** ``` 1. edit /etc/init/rc-sysinit.conf 2. env DEFAULT_RUNLEVEL=2 ``` ### **Become root** ``` su ``` ### **Become somebody** ``` su somebody ``` ### **Report user quotes on device** ``` repquota -auvs ``` ### **Get entries in a number of important databases** ``` getent database_name # (e.g. the 'passwd' database) getent passwd # list all user account (all local and LDAP) # (e.g. fetch list of grop accounts) getent group # store in database 'group' ``` ### **Change owner of file** ``` chown user_name filename chown -R user_name /path/to/directory/ # chown user:group filename ``` ### **Mount and unmount** ``` # e.g. Mount /dev/sdb to /home/test mount /dev/sdb /home/test # e.g. Unmount /home/test umount /home/test ``` ### **List current mount detail** ``` mount # or df ``` ### **List current usernames and user-numbers** ``` cat /etc/passwd ``` ### **Get all username** ``` getent passwd| awk '{FS="[:]"; print $1}' ``` ### **Show all users** ``` compgen -u ``` ### **Show all groups** ``` compgen -g ``` ### **Show group of user** ``` group username ``` ### **Show uid, gid, group of user** ``` id username # variable for UID echo $UID ``` ### **Check if it's root** ``` if [ $(id -u) -ne 0 ];then echo "You are not root!" exit; fi # 'id -u' output 0 if it's not root ``` ### **Find out CPU information** ``` more /proc/cpuinfo # or lscpu ``` ### **Set quota for user (e.g. disk soft limit: 120586240; hard limit: 125829120)** ``` setquota username 120586240 125829120 0 0 /home ``` ### **Show quota for user** ``` quota -v username ``` ### **Display current libraries from the cache** ``` ldconfig -p ``` ### **Print shared library dependencies (e.g. for 'ls')** ``` ldd /bin/ls ``` ### **Check user login** ``` lastlog ``` ### **Check last reboot history** ``` last reboot ``` ### **Edit path for all users** ``` joe /etc/environment # edit this file ``` ### **Show and set user limit** ``` ulimit -u ``` ### **Print out number of cores/ processors** ``` nproc --all ``` ### **Check status of each core** ``` 1. top 2. press '1' ``` ### **Show jobs and PID** ``` jobs -l ``` ### **List all running services** ``` service --status-all ``` ### **Schedule shutdown server** ``` shutdown -r +5 "Server will restart in 5 minutes. Please save your work." ``` ### **Cancel scheduled shutdown** ``` shutdown -c ``` ### **Broadcast to all users** ``` wall -n hihi ``` ### **Kill all process of a user** ``` pkill -U user_name ``` ### **Kill all process of a program** ``` kill -9 $(ps aux | grep 'program_name' | awk '{print $2}') ``` ### **Set gedit preference on server** ``` # You might have to install the following: apt-get install libglib2.0-bin; # or yum install dconf dconf-editor; yum install dbus dbus-x11; # Check list gsettings list-recursively # Change some settings gsettings set org.gnome.gedit.preferences.editor highlight-current-line true gsettings set org.gnome.gedit.preferences.editor scheme 'cobalt' gsettings set org.gnome.gedit.preferences.editor use-default-font false gsettings set org.gnome.gedit.preferences.editor editor-font 'Cantarell Regular 12' ``` ### **Add user to a group (e.g add user 'nice' to the group 'docker', so that he can run docker without sudo)** ``` sudo gpasswd -a nice docker ``` ### **Pip install python package without root** ``` 1. pip install --user package_name 2. You might need to export ~/.local/bin/ to PATH: export PATH=$PATH:~/.local/bin/ ``` ### **Removing old linux kernels (when /boot almost full...)** ``` 1. uname -a #check current kernel, which should NOT be removed 2. sudo apt-get purge linux-image-X.X.X-X-generic #replace old version ``` ### **Change hostname** ``` sudo hostname your-new-name # if not working, do also: hostnamectl set-hostname your-new-hostname # then check with: hostnamectl # Or check /etc/hostname # If still not working..., edit: /etc/sysconfig/network /etc/sysconfig/network-scripts/ifcfg-ensxxx #add HOSTNAME="your-new-hostname" ``` ### **List installed packages** ``` apt list --installed # or on Red Hat: yum list installed ``` ### **Check for package update** ``` apt list --upgradeable # or sudo yum check-update ``` ### **Run yum update excluding a package (e.g. do not update php packages)** ``` sudo yum update --exclude=php* ``` ### **Check which file make the device busy on umount** ``` lsof /mnt/dir ``` ### **When sound not working** ``` killall pulseaudio # then press Alt-F2 and type in pulseaudio ``` ### **When sound not working** ``` killall pulseaudio ``` ### **List information about SCSI devices** ``` lsscsi ``` ### **Tutorial for setting up your own DNS server** ### **Tutorial for creating a simple daemon** ### **Tutorial for using your gmail to send email** ### **Using telnet to test open ports, test if you can connect to a port (e.g 53) of a server (e.g 192.168.2.106)** ``` telnet 192.168.2.106 53 ``` ### **Change network maximum transmission unit (mtu) (e.g. change to 9000)** ``` ifconfig eth0 mtu 9000 ``` ### **Get pid of a running process (e.g python)** ``` pidof python # or ps aux|grep python ``` ### **Check status of a process using PID** ``` ps -p #or cat /proc//status cat /proc//stack cat /proc//stat ``` ### **NTP** ``` # Start ntp: ntpd # Check ntp: ntpq -p ``` ### **Remove unnecessary files to clean your server** ``` sudo apt-get autoremove sudo apt-get clean sudo rm -rf ~/.cache/thumbnails/* # Remove old kernal: sudo dpkg --list 'linux-image*' sudo apt-get remove linux-image-OLDER_VERSION ``` ### **Increase/ resize root partition (root partition is an LVM logical volume)** ``` pvscan lvextend -L +130G /dev/rhel/root -r # Adding -r will grow filesystem after resizing the volume. ``` ### **Create a UEFI Bootable USB drive (e.g. /dev/sdc1)** ``` sudo dd if=~/path/to/isofile.iso of=/dev/sdc1 oflag=direct bs=1048576 ``` ### **Locate and remove a package** ``` sudo dpkg -l | grep sudo dpkg --purge ``` ### **Create a ssh tunnel** ``` ssh -f -L 9000:targetservername:8088 root@192.168.14.72 -N #-f: run in background; -L: Listen; -N: do nothing #the 9000 of your computer is now connected to the 8088 port of the targetservername through 192.168.14.72 #so that you can see the content of targetservername:8088 by entering localhost:9000 from your browser. ``` ### **Get process ID of a process (e.g. sublime\_text)** ``` #pidof pidof sublime_text #pgrep, you don't have to type the whole program name pgrep sublim #pgrep, echo 1 if process found, echo 0 if no such process pgrep -q sublime_text && echo 1 || echo 0 #top, takes longer time top|grep sublime_text ``` ### **Some benchmarking tools for your server** [aio-stress](https://openbenchmarking.org/test/pts/aio-stress) - AIO benchmark.\ [bandwidth](https://zsmith.co/bandwidth.html) - memory bandwidth benchmark.\ [bonnie++](https://www.coker.com.au/bonnie++/) - hard drive and file system performance benchmark.\ [dbench](https://dbench.samba.org/) - generate I/O workloads to either a filesystem or to a networked CIFS or NFS server.\ [dnsperf](https://www.dnsperf.com/) - authorative and recursing DNS servers.\ [filebench](https://github.com/filebench/filebench) - model based file system workload generator.\ [fio](https://linux.die.net/man/1/fio) - I/O benchmark.\ [fs\_mark](https://github.com/josefbacik/fs_mark) - synchronous/async file creation benchmark.\ [httperf](https://github.com/httperf/httperf) - measure web server performance.\ [interbench](https://github.com/ckolivas/interbench) - linux interactivity benchmark.\ [ioblazer](https://labs.vmware.com/flings/ioblazer) - multi-platform storage stack micro-benchmark.\ [iozone](http://www.iozone.org/) - filesystem benchmark.\ [iperf3](https://iperf.fr/iperf-download.php) - measure TCP/UDP/SCTP performance.\ [kcbench](https://github.com/knurd/kcbench) - kernel compile benchmark, compiles a kernel and measures the time it takes.\ [lmbench](http://www.bitmover.com/lmbench/) - Suite of simple, portable benchmarks.\ [netperf](https://github.com/HewlettPackard/netperf) - measure network performance, test unidirectional throughput, and end-to-end latency.\ [netpipe](https://linux.die.net/man/1/netpipe) - network protocol independent performance evaluator.\ [nfsometer](http://wiki.linux-nfs.org/wiki/index.php/NFSometer) - NFS performance framework.\ [nuttcp](https://www.nuttcp.net/Welcome%20Page.html) - measure network performance.\ [phoronix-test-suite](https://www.phoronix-test-suite.com/) - comprehensive automated testing and benchmarking platform.\ [seeker](https://github.com/fidlej/seeker) - portable disk seek benchmark.\ [siege](https://github.com/JoeDog/siege) - http load tester and benchmark.\ [sockperf](https://github.com/Mellanox/sockperf) - network benchmarking utility over socket API.\ [spew](https://linux.die.net/man/1/spew) - measures I/O performance and/or generates I/O load.\ [stress](https://people.seas.harvard.edu/~apw/stress/) - workload generator for POSIX systems.\ [sysbench](https://github.com/akopytov/sysbench) - scriptable database and system performance benchmark.\ [tiobench](https://github.com/mkuoppal/tiobench) - threaded IO benchmark.\ [unixbench](https://github.com/kdlucas/byte-unixbench) - the original BYTE UNIX benchmark suite, provide a basic indicator of the performance of a Unix-like system.\ [wrk](https://github.com/wg/wrk) - HTTP benchmark. ### **Performance monitoring tool - sar** ``` # installation # It collects the data every 10 minutes and generate its report daily. crontab file (/etc/cron.d/sysstat) is responsible for collecting and generating reports. yum install sysstat systemctl start sysstat systemctl enable sysstat # show CPU utilization 5 times every 2 seconds. sar 2 5 # show memory utilization 5 times every 2 seconds. sar -r 2 5 # show paging statistics 5 times every 2 seconds. sar -B 2 5 # To generate all network statistic: sar -n ALL # reading SAR log file using -f sar -f /var/log/sa/sa31|tail ``` ### **Reading from journal file** ``` journalctl --file ./log/journal/a90c18f62af546ccba02fa3734f00a04/system.journal --since "2020-02-11 00:00:00" ``` ### **Show a listing of last logged in users.** ``` lastb ``` ### **Show a listing of current logged in users, print information of them** ``` who ``` ### **Show who is logged on and what they are doing** ``` w ``` ### **Print the user names of users currently logged in to the current host.** ``` users ``` ### **Stop tailing a file on program terminate** ``` tail -f --pid= filename.txt # replace with the process ID of the program. ``` ### **List all enabled services** ``` systemctl list-unit-files|grep enabled ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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