Process management

The following are common commands and utilities for process management in Linux.

1 Process management

Command	Function
at -d job ID	Cancels scheduled job according to job ID; equivalent to atrm
at -l cmd	Lists scheduled jobs; equivalent to atq
at time cmd	Runs a command at a specified time
bg	Moves a running process to the background.
bpytop	A new top alternative (requires installation)
cmd &	Start a process and send it to the background
crontab -e	Edit crontable
crontab -l	List scheduled tasks
crontab -r	Remove crontable
df	Display information on system disks, e.g., free and used storage
dmesg -k	Outputs system messages (helpful for troubleshooting)
dmesg -k	Display system messages
fg	Brings the most recent background job to the foreground
fg PID	Brings a job to the foreground
free	Display information about RAM and swap, free and used memory.
fuser	Show which processes are using a particular file, device, or system resource
fuser -m /dev/sda1	Show which processes are using a particular device
history	Print a history list of all commands issued within a particular shell
htop	Display all running processes in real time (alternative to top)
jobs	List all jobs presently running
journalctl	System logs
journalctl _UID=1000	View log entries for a specific user by user ID
journalctl --since "YYYY-MM-DD HH:MM" --until "YYYY-MM-DD HH:MM"	Filter and display log entries for a certain time period
journalctl -f	Follow system logs in real time
journalctl -u httpd -n 3	View 3 log entries for httpd
journalctl -u sshd	View log entries for only SSH
kill	Terminate a running process.
kill -1 OR -15	Soft kill a process
kill -2	Interrupt process; equivalent to CTL-c
kill -9	Kill a process forcefully and immediately
kill -l	List kill signal names
kill PID	Kills a running process of a specified process ID.
killall procname	Kill all processes of the specified name
lsof	List all files opened by running processes
lsof	Display currently open files
nice	Grant execution rights to a process with an assigned priority.
nohup	Allow a process to continue after logging out
pidof	Shows the process ID of a specified process.
pidof procname	Find the PID of a process
ps	Display currently running processes
ps -ef	Display all active processes
grep procname	Display information on a specific process
ps aux	Display information on running processes in BSD format
ps PID	Display the status of a running processes by its process ID
pstree	Display processes in the tree-like diagram
renice	Change or alter the execution priority of an already running system process
renice -5 PID	Adjust priority level of a running process by process ID
script	Record terminal session activity and create output for the session in a file
sensors	Outputs the system's CPU temperature
stop\|restart	Used for managing system services through an executable sysV init script. You can start, stop, or restart the specified system service.
systemctl status service	Change the status of a service managed by systemctl
time	Print time taken for a command to finish running
top	Manage and display all processes in real time
whereis	Show locations of binary, source and manual pages for a command
which program	Show the commands associated with an application

2 Rsync

Command	Function
rsycn -av –exclude ‘*.txt’ /src_dir/ /dest_dir	Archive but exclude a specific file type
rsync -av --max-size=1000m src_dir/ dest_dir/	Archive but exclude files over a certain size
rsync -av –exclude ‘dir’ /src_dir/ /dest_dir	Archive but exclude a specific directory from the source location
rsync -av /src_dir/ dest_dir	Archival backup (recursively, preserving links and file attributes; v=verbose)
rsync -avR /a/b/xyz.c remote:/tmp/	Archive a file on a remote machine, preserving the relative path (e.g., creating /tmp/a/b/xyz.c)
rsync -avz /src_dir/ /dest_dir	Archive as a compressed file
rsync /source_dir/ /desitnation_dir OR source_dir/ destination_dir/	Backup a directory to a different location

3 Crontab

Crontab is a utility to schedule and automate processes and commands. To get started setting up Crontab to automate processes, you can invoke the editor and do some general management like so. If you've set up a command and want to end the process, you need to open up the crontab editor, delete the entry, and save the crontab file (saving it will restart the crond daemon). The cron editor on many systems may use the vi editor by default, and some experienced users insist one should use vi.

Command	Function
crontab -e	Edit crontab file
EDITOR=nano crontab -e	Specify an editor like nano to edit the crontab file
crontab -l	List the scheduled crontab jobs
crontab -r	Remove the crontab file
crontab -v	Display the last time the crontab file was edited

In the crontabe editor, the following crontab syntax is used to set up automatic processes. The columns are in the following owrder:

Command
Minute (0-59)
Hour (0-23, 0=midnight)
Day of the month (1-31)
Month (1-12)
Day of the week (0-6, 0=Sunday)

Min (0-59)	Hour (0-23)	Day/month (1-31)	Month (1-12)	Day of week (0-6; Sunday=0)	Command	#Explanation
*	*	*	*	*	*	#Default (Null contents when first starting crontab)
0	20	*	*	*	rm /home/user/dir/*	#Remove files from a specified directory every day at 8pm
30	*	*	*	*	rm /home/user/dir/*	#Removes contents of a specified directory every our on the half hour
0	0	1	*	*	rsynch -azv /home/user/ /bk/user	#Automated archival backup of a user’s home directory every month (at midnight at the start of each month)
0	0	*	*	0	rsynch -azv /home/user/ /bk/user	#Automated archival backup every Sunday at midnight
0	22	*	*	1-5	rsynch -azv /home/user/ /bk/user > /dev/null 2>&1	#Automated archival backup at 10pm every weekday; then prevent crontab from sending an email to the user account (by default, cron sends an email after executing each command)
0	0	*	*	*	rsynch -azv /home/user/ /bk/user > /home/users/crontlogs/cron.log	#Automated archival backup; and log each job in a file