proc - running processes
bind #p /proc
The proc device serves a two-level directory structure. The first level contains numbered
directories corresponding to pids of live processes; each such directory contains a set of
files representing the corresponding process.
The mem file contains the current memory image of the process. A read or write at offset
o, which must be a valid virtual address, accesses bytes from address o up to the end of
the memory segment containing o. Kernel virtual memory, including the kernel stack for
the process and saved user registers (whose addresses are machine-dependent), can be
accessed through mem. Writes are permitted only while the process is in the Stopped state
and only to user addresses or registers.
The read-only proc file contains the kernel per-process structure. Its main use is to
recover the kernel stack and program counter for kernel debugging.
The read-only segment file contains a textual display of the memory segments attached to
the process. Each line has multiple fields: the type of segment (Stack, Text, Data, Bss,
etc.); one-letter flags such as R for read-only, if any; starting virtual address, in
hexadecimal; ending virtual address, and reference count.
The read-only status file contains a string with eight fields, each followed by a space.
The fields are: the process name and user name, each 27 characters left justified; the
process state, 11 characters left justified (see ps(1)); the six 11-character numbers also
held in the process's #c/cputime file, and the amount of memory used by the process,
except its stack, in units of 1024 bytes.
The text file is a pseudonym for the file from which the process was executed; its main
use is to recover the symbol table of the process.
The wait file may be read to recover Waitmsg records from the exiting children of the
process. If the process has no extant children, living or exited, a read of wait will
block. It is an error for a process to attempt to read its own wait file when it has no
children. When a process's wait file is being read, the process will draw an error if it
attempts a wait system call; similarly, if a process is in a wait system call, its wait
file cannot be read by any process.
Textual messages written to the ctl file control the execution of the process. Some
require that the process is in a particular state and return an error if it is not.
stop Suspend execution of the process, putting it in the Stopped state.
start Resume execution of a Stopped process.
waitstop Do not affect the process directly but, like all other messages ending with
stop, block the process writing the ctl file until the target process is in the
Stopped state or exits. Also like other stop control messages, if the target
process would receive a note while the message is pending, it is instead stopped
and the debugging process is resumed.
startstop Allow a Stopped process to resume, and then do a waitstop action.
hang Set a bit in the process so that, when it completes an exec(2) system call, it
will enter the Stopped state before returning to user mode. This bit is inher-
ited across a fork(2).
nohang Clear the hang bit.
kill Kill the process the next time it crosses the user/kernel boundary.
Strings written to the note file will be posted as a note to the process (see notify(2)).
The note should be less than characters long; the last character is reserved for a termi-
nating NUL character. A read of at least characters will retrieve the oldest note posted
to the process and prevent its delivery to the process. The notepg file is similar, but
the note will be delivered to all the processes in the target process's note group (see
fork(2)). However, if the process doing the write is in the group, it will not receive
the note. The notepg file is write-only.
The textual noteid file may be read to recover an integer identifying the note group of
the process (see RFNOTEG in fork(2)). The file may be written to cause the process to
change to another note group, provided the group exists and is owned by the same user.
debugger(2), mach(2), cons(3)