File descriptors - Revision history

Pbug: /* How do I see descriptors of a process? */

2008-02-25T20:06:13Z

How do I see descriptors of a process?

← Older revision		Revision as of 13:06, 25 February 2008
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	== How do I see descriptors of a process? ==		== How do I see descriptors of a process? ==


			=== OpenBSD ===
	There are a number of ways to see the open file descriptors of another program. In [[BSD]] the fstat(1) command lists all running programs (processes) of the system and their open descriptors furthermore it lists what type of descriptor it is (file, socket, pipe, etc) and tries to give a hint of what the descriptor is reading or writing on such as what filesystem and what inode number on that file system. In [[OpenBSD]] network sockets display what port number they have open which is useful for finding the program of that port. See [[ports]]:		There are a number of ways to see the open file descriptors of another program. In [[BSD]] the fstat(1) command lists all running programs (processes) of the system and their open descriptors furthermore it lists what type of descriptor it is (file, socket, pipe, etc) and tries to give a hint of what the descriptor is reading or writing on such as what filesystem and what inode number on that file system. In [[OpenBSD]] network sockets display what port number they have open which is useful for finding the program of that port. See [[ports]]:

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			=== Linux ===

	~~----~~

	In [[Linux]] you'd use lsof to dig through the /proc filesystem to see open descriptors / [[ports]]. Specifically, you want to look in the /proc/<PID>/fd directory. Each symlink will point to an open file/socket/etc. An example from [[xterm]]:		In [[Linux]] you'd use lsof to dig through the /proc filesystem to see open descriptors / [[ports]]. Specifically, you want to look in the /proc/<PID>/fd directory. Each symlink will point to an open file/socket/etc. An example from [[xterm]]:

Sysadmin at 05:16, 25 October 2005

2005-10-25T05:16:31Z

← Older revision		Revision as of 22:16, 24 October 2005
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	----		----

	In [[Linux]] you'd use lsof to dig through the /proc filesystem to see open descriptors / [[ports]]. Specifically, you want to look in the /proc/<PID>/fd directory. ~~ZEach~~ symlink will point to an open file/socket/etc. An example from [[xterm]]:		In [[Linux]] you'd use lsof to dig through the /proc filesystem to see open descriptors / [[ports]]. Specifically, you want to look in the /proc/<PID>/fd directory. Each symlink will point to an open file/socket/etc. An example from [[xterm]]:

	jbecker@aubrey /space/winders $ ls -l /proc/9383/fd		jbecker@aubrey /space/winders $ ls -l /proc/9383/fd

Hawson at 14:56, 15 October 2005

2005-10-15T14:56:10Z

← Older revision		Revision as of 07:56, 15 October 2005
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	----		----

	In [[Linux]] you'd use lsof or dig through the /proc filesystem to see open descriptors / [[ports]].		In [[Linux]] you'd use lsof to dig through the /proc filesystem to see open descriptors / [[ports]]. Specifically, you want to look in the /proc/<PID>/fd directory. ZEach symlink will point to an open file/socket/etc. An example from [[xterm]]:

			jbecker@aubrey /space/winders $ ls -l /proc/9383/fd
			total 6
			lr-x------ 1 jbecker users 64 Oct 15 09:53 0 -> /dev/null
			l-wx------ 1 jbecker users 64 Oct 15 09:53 1 -> /home/jbecker/.xsession-errors
			l-wx------ 1 jbecker users 64 Oct 15 09:53 2 -> /home/jbecker/.xsession-errors
			l-wx------ 1 jbecker users 64 Oct 15 09:53 3 -> /home/jbecker/.fluxbox/log
			lrwx------ 1 jbecker users 64 Oct 15 09:53 4 -> socket:[2995011]
			lrwx------ 1 jbecker users 64 Oct 15 09:53 5 -> /dev/ptmx

Pbug: /* How do I see descriptors of a process? */

2005-10-15T12:38:53Z

How do I see descriptors of a process?

← Older revision		Revision as of 05:38, 15 October 2005
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	Below you'll find a list of descriptors of different types as well as examples what to do with the information given by fstat (this example uses fstat from [[OpenBSD]]:		Below you'll find a list of descriptors of different types as well as examples what to do with the information given by fstat (this example uses fstat from [[OpenBSD]]):

Pbug: /* How do I see descriptors of a process? */

2005-10-15T12:30:01Z

How do I see descriptors of a process?

← Older revision		Revision as of 05:30, 15 October 2005
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	There are a number of ways to see the open file descriptors of another program. In [[BSD]] the fstat(1) command lists all running programs (processes) of the system and their open descriptors furthermore it lists what type of descriptor it is (file, socket, pipe, etc) and tries to give a hint of what the descriptor is reading or writing on such as what filesystem and what inode number on that file system. In [[OpenBSD]] network sockets display what port number they have open which is useful for finding the program of that port. See [[ports]]:		There are a number of ways to see the open file descriptors of another program. In [[BSD]] the fstat(1) command lists all running programs (processes) of the system and their open descriptors furthermore it lists what type of descriptor it is (file, socket, pipe, etc) and tries to give a hint of what the descriptor is reading or writing on such as what filesystem and what inode number on that file system. In [[OpenBSD]] network sockets display what port number they have open which is useful for finding the program of that port. See [[ports]]:


			Below you'll find a list of descriptors of different types as well as examples what to do with the information given by fstat (this example uses fstat from [[OpenBSD]]:


	In fstat a filedescriptor on a file looks like this:		In fstat a filedescriptor on a file looks like this:

Pbug: /* How do I see descriptors of a process? */

2005-10-15T12:00:11Z

How do I see descriptors of a process?

← Older revision		Revision as of 05:00, 15 October 2005
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	USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ		USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ
	root sshd 3641 5* internet stream tcp 0xfffffe800f551008 *:22		root sshd 3641 5* internet stream tcp 0xfffffe800f551008 *:22
			...
			$ netstat -naA \| head -2
			Active Internet connections (including servers)
			PCB Proto Recv-Q Send-Q Local Address Foreign Address (state)
			$ netstat -naA \| awk '$1 == "0xfffffe800f551008" { print }'
			0xfffffe800f551008 tcp 0 0 .22 .* LISTEN


	A connected Internet socket descriptor looks like this:		A connected Internet socket descriptor looks like this:

Pbug: /* How do I see descriptors of a process? */

2005-10-15T11:44:42Z

How do I see descriptors of a process?

← Older revision		Revision as of 04:44, 15 October 2005
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	USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ		USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ
	bituser python2.3 5233 26 /usr 9050558 -rw-r--r-- rw 48758784		bituser python2.3 5233 26 /usr 9050558 -rw-r--r-- rw 48758784
			...
			$ find /usr/home/bituser -inum 9050558 -print 2>/dev/null
			/usr/home/bituser/downloads/trusted-computing/TrustedComputing_LAFKON_HIGH.mov

	An Internet socket that's listening looks like this:		An Internet socket that's listening looks like this:

Pbug: /* Descriptors */

2005-10-15T11:40:40Z

Descriptors

← Older revision		Revision as of 04:40, 15 October 2005
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	When a new [[process]] is created (by means of the [[fork]](2) system call) it inherits all open descriptors from the parent process. New descriptors are made by the following system calls [[open]](2), [[pipe]](2), [[socket]](2), [[accept]](2) and [[socketpair]](2). A descriptor can be duplicated thus creating a new descriptor and number with the dup(2) system call. A descriptor can be destroyed by means of the close(2) system call. All programs executed from a shell have the following 3 descriptors open bound to the terminal: [[Stdin]], [[Stdout]] and [[Stderr]], representing descriptor numbers 0, 1 and 2 respectively. More about descriptors can be found in the fd [[manual]] page on the [[OpenBSD]] system; "man 4 fd" to see this.		When a new [[process]] is created (by means of the [[fork]](2) system call) it inherits all open descriptors from the parent process. New descriptors are made by the following system calls [[open]](2), [[pipe]](2), [[socket]](2), [[accept]](2) and [[socketpair]](2). A descriptor can be duplicated thus creating a new descriptor and number with the dup(2) system call. A descriptor can be destroyed by means of the close(2) system call. All programs executed from a shell have the following 3 descriptors open bound to the terminal: [[Stdin]], [[Stdout]] and [[Stderr]], representing descriptor numbers 0, 1 and 2 respectively. More about descriptors can be found in the fd [[manual]] page on the [[OpenBSD]] system; "man 4 fd" to see this.

	Careful plumbing done by a program (such as a user shell) can use the pipe(2), [[fork]](2), [[exec]](2) and [[dup2]](2) syscalls to connect the [[stdout]] of one program with [[stdin]] of another program this is called piping (see [[pipe]]). Long [[pipe]] chains (proper: pipelines) can be created this way.		Careful plumbing done by a program (such as a user shell) can use the [[pipe]](2), [[fork]](2), [[exec]](2) and [[dup2]](2) syscalls to connect the [[stdout]] of one program with [[stdin]] of another program this is called piping (see [[pipe]]). Long [[pipe]] chains (proper: pipelines) can be created this way.

	When a program becomes a [[daemon]] [[stdin]], [[stdout]] and [[stderr]] are usually closed and attached to the [[null]] device since they don't have a controlling terminal anymore. All writes to these descriptors will be discarded.		When a program becomes a [[daemon]] [[stdin]], [[stdout]] and [[stderr]] are usually closed and attached to the [[null]] device since they don't have a controlling terminal anymore. All writes to these descriptors will be discarded.

Pbug at 11:39, 15 October 2005

2005-10-15T11:39:45Z

← Older revision		Revision as of 04:39, 15 October 2005
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	USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ		USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ
	root ntpd 12284 3* unix stream 0xffff800001cd6480 <-> 0xffff800001cd6700		root ntpd 12284 3* unix stream 0xffff800001cd6480 <-> 0xffff800001cd6700

			A desriptor to a pipe looks like this:
			USER CMD PID FD MOUNT INUM MODE R/W DV\|SZ
			pbug fstat 26338 1 pipe 0xfffffe801f525d28 state:

	A descriptor on a fifo looks like this:		A descriptor on a fifo looks like this:

Pbug: /* How do I see descriptors of a process? */

2005-10-15T10:57:16Z

How do I see descriptors of a process?

@@ Line 22: / Line 22: @@
 There are a number of ways to see the open file descriptors of another program.  In [[BSD]] the fstat(1) command lists all running programs (processes) of the system and their open descriptors furthermore it lists what type of descriptor it is (file, socket, pipe, etc) and tries to give a hint of what the descriptor is reading or writing on such as what filesystem and what inode number on that file system.  In [[OpenBSD]] network sockets display what port number they have open which is useful for finding the program of that port.  See [[ports]]:
 ----
 In [[Linux]] you'd use lsof or dig through the /proc filesystem to see open descriptors / [[ports]].