# Chapter 3. kpm main window

# 3.1. Explaining the fields

PID - Process ID

  Each process has a unique process ID number, starting at 1 and going up. When a new process is created, the next unused PID is allocated. PIDs are (currently) 16-bit signed integers, so they wrap around at 32767; this is normal behaviour and nothing to worry about.

PPID - Parent process ID

  Every process has one parent process. The exception is process 1 (init), which is the root of the process hierarchy; it has no parent.

PGID - Process group ID

  Each process is member of one process group. Process groups are used for distribution of signals, and by terminals to arbitrate requests for their input: processes that have the same process group as the terminal are foreground and may read, while others will block with a signal if they attempt to read.

SID - Session ID

  Session IDs are used mainly to determine what happens at terminal hangups.

TTY - Controlling tty

  The controlling terminal (tty) is usually the device (serial port, pty etc) from which the process was started, and which it uses for input or output. Not all processes have a controlling terminal. Kpm scans the /dev directory to determine the name of the terminal, but this might fail. To save space, only the two last characters of the tty name is shown (thus /dev/ttyp6 is shown as p6)

TPGID - Process group ID of tty owner

  A tty in use is owned by a process. This is the PGID of that process.

USER - Process owner

  This is the name of the (real) user owning the process. If the effective user ID of a process is different from the real user ID, this is indicated by a trailing "*" or "+". The asterisk is used when the effective user is the super-user (this usually indicates a binary that is set-uid to root).

NICE - Time-sharing priority

  The nice value determines how often a process is allowed to run, and the length of its timeslice. The value is in the range -20 to 20, 0 being the default. Lower numbers give more CPU time to a process. Only the super-user may lower the nice value.

PRI - Length of next timeslice

  This is the maximal length of the process's next timeslice (or what is left of its current timeslice, if it is the currently running process). The number is rescaled to the -20..20 interval, smaller number indicating a longer timeslice.

PLCY - Scheduling policy

  FIFO (F) and Round-Robin (R) are realtime scheduling policies; OTHER (O) is the normal Unix time-sharing policy. F and R processes have a realtime priority between 1 and 99. A process will run as long as there is no runnable process with higher priority. Round-Robin processes will run for the length of one time-slice, after which they are placed last in the queue of their priority. FIFO processes run until they give up their CPU time (by sleeping or blocking) or pre-empted by a process with higher priority. Only the super-user (root) may change the scheduling policy.

RPRI - Realtime priority

  Realtime processes (FIFO and Round-Robin) have priorities between 1 and 99. A process will pre-empt any other process that has lower priority. Normal time-sharing processes (policy O) all have priority 0. Only the super-user (root) may change the realtime priority.

MAJFLT - Number of major faults occured

  A page fault occurs when a process attempts to read or write from a memory page that isn't present in RAM. A major page fault is when disk access is involved, such as swapping in and out memory pages.

MINFLT - Number of minor faults occured

  A page fault occurs when a process attempts to read or write from a memory page that isn't present in RAM, or write to a page that isn't writeable. A minor fault is when there is no disk access involved, for instance when writing to a copy-on-write shared page.

TRS - Text resident set size (Kbytes)

  This is the size of the text (that is, executable code) of the process that is currently present in RAM.

DRS - Data resident set size (Kbytes)

  This is the size of the data (not executable code) of the process that is currently present in RAM.

SIZE - virtual image size of process (Kbytes)

  This is the total size of the image of the process. This includes all code, data, and shared libraries used by the process, including pages that have been swapped out.

SWAP - Kbytes on swap device

  This is simply the difference between SIZE and RSS, in other words how much of a process that resides on disk.

RSS - resident set size (Kbytes)

  This is the size of the part of the process (code and data) that actually resides in RAM, including shared libraries. This gives a fair approximation of how much RAM a process is using.

SHARE - shared memory (Kbytes)

  This is the amount of memory that the process shares with other processes. It doesn't mean that any of it is actually used by any other process, just that it is possible.

DT - number of dirty pages

  This is the number (not the number of bytes!) of pages in RAM that have been modified since they were last written to disk. Dirty pages have to be written to disk before they are freed and used for something else.

STAT - state of the process

  The process is at any time in one of the following states:

  - R (running): the process is running on a cpu or is ready to run.

  - S (sleeping): the process is waiting for an event to occur (such as I/O or a timer).

  - D (uninterruptible sleep): the process is waiting for an event to occur, without being interruptible (usually waiting in a device driver).

  - T (stopped): the process is stopped, or being traced by another process.

  - Z (zombie): the process has terminated, but its parent hasn't mourned its death yet.

  - If the process is completely swapped out (has no resident pages), a 'W' is shown in the field. (This is also true for kernel processes, such as kswapd.)

FLAGS - process flags (hex)

  This contains some additional information about the state of a process. Refer to the Linux kernel source for details.

WCHAN - function where process is sleeping

  If the process is waiting for something to happen, this is the kernel function where it is stuck. (Leading do_ or sys_ is stripped from the name to make it shorter.)

UID - numerical user ID

  This is the ID of the (real) user owning the process.

%WCPU - weighted percentage of CPU

  This is the percentage of CPU time the process is using, averaged over the last 30 seconds (exponentially decaying average).

%CPU - percentage of CPU since last update

  This is how much of the CPU time the process used since the last update of kpm's process table.

%MEM - percentage of memory used

  This is how large part of the total RAM that is used by the process (as resident size). Shared libraries count, so this is an overstatement.

START - time process started

  This is when the process was created.

TIME - total CPU time used

  This is how much CPU time the process has used since it was started.

COMM - command that started the process

  This is the command (file name) that started the process. Long names are truncated.

CMDLINE - command line that started the process

  This the command line, including arguments, that started the process. If "Hide Command Path" in the Options menu is selected, then the leading path of the command name is stripped. Processes swapped out may show just the command name in parentheses (this is true for kernel processes as well).