Usage:
top -hv | -bcHiOSs -d secs -n max -u|U user -p pid(s) -o field -w [cols]
The command top display the system summary information that is organized on 5 areas.
The first area display the current time, the time since last boot, the total number of users, the system load average over the last 1, 5 and 15 minutes.
The second area display the number of processes and how much of them are running, sleeping, stopped, zombie.
The last areas display information about the CPU, the physical memory, and the swap memory.

The command top also display a detailed list of all running processes.
By default the list provides the following headers:

• PID: the process id.
  
• USER: the owner of the process.
  
• PR: the priority of the process.
  
• NI: the nice value of the process.
  
• VIRT: the virtual memory used by the process.
  
• RES: the physical memory used by the process.
  
• SHR: the shared memory with other processes.
  
• S: the process status (D: uninterruptible sleep, R: running, S: sleeping, T: stopped by job control signal, t: stopped by debugger during trace, Z: zombie).
  
• %CPU: the share of CPU time that the process is suing.
  
• %MEM: the share of physical memory that the process is suing.
  
• TIME+: the CPU time used by the process.
  
• COMMAND: the command line used to start the process.
  

$ top top - 17:23:08 up 1 day, 6:10, 1 user, load average: 0.11, 0.04, 0.01 Tasks: 226 total, 1 running, 159 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.2 us, 0.1 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st KiB Mem : 32654668 total, 29423936 free, 798248 used, 2432484 buff/cache KiB Swap: 37109756 total, 37109756 free, 0 used. 31335344 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1602 root 20 0 1570844 46868 26052 S 0.7 0.1 1:09.06 containerd 1595 mongodb 20 0 1583628 106204 38000 S 0.3 0.3 9:02.59 mongod 1792 mysql 20 0 1426572 181280 15792 S 0.3 0.6 1:21.88 mysqld ...
By default the list is sorted using the %CPU column.
To change the headers (add or remove) and/or adjust the sort column, press the key 'f'.
Navigate with Up/Dn.
Press the key 'd' or <space> to add or remove a header.
Press the key 's' to apply changes.
Press the key 'q' or <esc> to exit.

Fields Management for window 1:Def, whose current sort field is %CPU Navigate with Up/Dn, Right selects for move then <Enter> or Left commits, 'd' or <Space> toggles display, 's' sets sort. Use 'q' or <Esc> to end! * PID = Process Id ENVIRON = Environment vars * USER = Effective User Name vMj = Major Faults delta * PR = Priority vMn = Minor Faults delta * NI = Nice Value USED = Res+Swap Size (KiB) * VIRT = Virtual Image (KiB) nsIPC = IPC namespace Inode * RES = Resident Size (KiB) nsMNT = MNT namespace Inode * SHR = Shared Memory (KiB) nsNET = NET namespace Inode * S = Process Status nsPID = PID namespace Inode * %CPU = CPU Usage nsUSER = USER namespace Inode * %MEM = Memory Usage (RES) nsUTS = UTS namespace Inode * TIME+ = CPU Time, hundredths LXC = LXC container name * COMMAND = Command Name/Line RSan = RES Anonymous (KiB) PPID = Parent Process pid RSfd = RES File-based (KiB) UID = Effective User Id RSlk = RES Locked (KiB) RUID = Real User Id RSsh = RES Shared (KiB) RUSER = Real User Name CGNAME = Control Group name SUID = Saved User Id SUSER = Saved User Name GID = Group Id GROUP = Group Name PGRP = Process Group Id TTY = Controlling Tty TPGID = Tty Process Grp Id SID = Session Id nTH = Number of Threads P = Last Used Cpu (SMP) TIME = CPU Time SWAP = Swapped Size (KiB) CODE = Code Size (KiB) DATA = Data+Stack (KiB) nMaj = Major Page Faults nMin = Minor Page Faults nDRT = Dirty Pages Count WCHAN = Sleeping in Function Flags = Task Flags <sched.h> CGROUPS = Control Groups SUPGIDS = Supp Groups IDs SUPGRPS = Supp Groups Names TGID = Thread Group Id OOMa = OOMEM Adjustment OOMs = OOMEM Score current