27.2. /proc
The /proc directory is actually a pseudo-filesystem. The files in /proc mirror currently running system and kernel processes and contain information and statistics about them.
bash$ cat /proc/devices
Character devices:
1 mem
2 pty
3 ttyp
4 ttyS
5 cua
7 vcs
10 misc
14 sound
29 fb
36 netlink
128 ptm
136 pts
162 raw
254 pcmcia
Block devices:
1 ramdisk
2 fd
3 ide0
9 md
bash$ cat /proc/interrupts
CPU0
0: 84505 XT-PIC timer
1: 3375 XT-PIC keyboard
2: 0 XT-PIC cascade
5: 1 XT-PIC soundblaster
8: 1 XT-PIC rtc
12: 4231 XT-PIC PS/2 Mouse
14: 109373 XT-PIC ide0
NMI: 0
ERR: 0
bash$ cat /proc/partitions
major minor #blocks name rio rmerge rsect ruse wio wmerge wsect wuse running use aveq
3 0 3007872 hda 4472 22260 114520 94240 3551 18703 50384 549710 0 111550 644030
3 1 52416 hda1 27 395 844 960 4 2 14 180 0 800 1140
3 2 1 hda2 0 0 0 0 0 0 0 0 0 0 0
3 4 165280 hda4 10 0 20 210 0 0 0 0 0 210 210
...
bash$ cat /proc/loadavg
0.13 0.42 0.27 2/44 1119
bash$ cat /proc/apm
1.16 1.2 0x03 0x01 0xff 0x80 -1% -1 ?
bash$ cat /proc/acpi/battery/BAT0/info
present: yes
design capacity: 43200 mWh
last full capacity: 36640 mWh
battery technology: rechargeable
design voltage: 10800 mV
design capacity warning: 1832 mWh
design capacity low: 200 mWh
capacity granularity 1: 1 mWh
capacity granularity 2: 1 mWh
model number: IBM-02K6897
serial number: 1133
battery type: LION
OEM info: Panasonic
bash$ fgrep Mem /proc/meminfo
MemTotal: 515216 kB
MemFree: 266248 kB
|
Shell scripts may extract data from certain of the files in /proc. [1]
1 FS=iso # ISO filesystem support in kernel? 2 3 grep $FS /proc/filesystems # iso9660 |
1 kernel_version=$( awk '{ print $3 }' /proc/version ) |
1 CPU=$( awk '/model name/ {print $5}' < /proc/cpuinfo )
2
3 if [ "$CPU" = "Pentium(R)" ]
4 then
5 run_some_commands
6 ...
7 else
8 run_different_commands
9 ...
10 fi
11
12
13
14 cpu_speed=$( fgrep "cpu MHz" /proc/cpuinfo | awk '{print $4}' )
15 # Current operating speed (in MHz) of the cpu on your machine.
16 # On a laptop this may vary, depending on use of battery
17 #+ or AC power. |
1 #!/bin/bash
2 # get-commandline.sh
3 # Get the command-line parameters of a process.
4
5 OPTION=cmdline
6
7 # Identify PID.
8 pid=$( echo $(pidof "$1") | awk '{ print $1 }' )
9 # Get only first
of multiple instances.
10
11 echo
12 echo "Process ID of (first instance of) "$1" = $pid"
13 echo -n "Command-line arguments: "
14 cat /proc/"$pid"/"$OPTION" | xargs -0 echo
15 # Formats output:
16 # (Thanks, Han Holl, for the fixup!)
17
18 echo; echo
19
20
21 # For example:
22 # sh get-commandline.sh xterm |
+
1 devfile="/proc/bus/usb/devices"
2 text="Spd"
3 USB1="Spd=12"
4 USB2="Spd=480"
5
6
7 bus_speed=$(fgrep -m 1 "$text" $devfile | awk '{print $9}')
8 #
Stop after first match.
9
10 if [ "$bus_speed" = "$USB1" ]
11 then
12 echo "USB 1.1 port found."
13 # Do something appropriate for USB 1.1.
14 fi |
 |
It is even possible to control certain peripherals with commands sent to the /proc directory.
Of course, caution is advised when writing to /proc. |
The /proc directory contains subdirectories with unusual numerical names. Every one of these names maps to the process ID of a currently running process. Within each of these subdirectories, there are a number of files that hold useful information about the corresponding process. The stat and status files keep running statistics on the process, the cmdline file holds the command-line arguments the process was invoked with, and the exe file is a symbolic link to the complete path name of the invoking process. There are a few more such files, but these seem to be the most interesting from a scripting standpoint.
Example 27-2. Finding the process associated with a PID
1 #!/bin/bash
2 # pid-identifier.sh:
3 # Gives complete path name to process associated with pid.
4
5 ARGNO=1 # Number of arguments the script expects.
6 E_WRONGARGS=65
7 E_BADPID=66
8 E_NOSUCHPROCESS=67
9 E_NOPERMISSION=68
10 PROCFILE=exe
11
12 if [ $# -ne $ARGNO ]
13 then
14 echo "Usage: `basename $0` PID-number" >&2 # Error message >stderr.
15 exit $E_WRONGARGS
16 fi
17
18 pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 )
19 # Checks for pid in "ps" listing, field #1.
20 # Then makes sure it is the actual process, not the process invoked by this script.
21 # The last "grep $1" filters out this possibility.
22 #
23 # pidno=$( ps ax | awk '{ print $1 }' | grep $1 )
24 # also works, as Teemu Huovila, points out.
25
26 if [ -z "$pidno" ] # If, after all the filtering, the result is a zero-length string,
27 then #+ no running process corresponds to the pid given.
28 echo "No such process running."
29 exit $E_NOSUCHPROCESS
30 fi
31
32 # Alternatively:
33 # if ! ps $1 > /dev/null 2>&1
34 # then # no running process corresponds to the pid given.
35 # echo "No such process running."
36 # exit $E_NOSUCHPROCESS
37 # fi
38
39 # To simplify the entire process, use "pidof".
40
41
42 if [ ! -r "/proc/$1/$PROCFILE" ] # Check for read permission.
43 then
44 echo "Process $1 running, but..."
45 echo "Can't get read permission on /proc/$1/$PROCFILE."
46 exit $E_NOPERMISSION # Ordinary user can't access some files in /proc.
47 fi
48
49 # The last two tests may be replaced by:
50 # if ! kill -0 $1 > /dev/null 2>&1 # '0' is not a signal, but
51 # this will test whether it is possible
52 # to send a signal to the process.
53 # then echo "PID doesn't exist or you're not its owner" >&2
54 # exit $E_BADPID
55 # fi
56
57
58
59 exe_file=$( ls -l /proc/$1 | grep "exe" | awk '{ print $11 }' )
60 # Or exe_file=$( ls -l /proc/$1/exe | awk '{print $11}' )
61 #
62 # /proc/pid-number/exe is a symbolic link
63 #+ to the complete path name of the invoking process.
64
65 if [ -e "$exe_file" ] # If /proc/pid-number/exe exists,
66 then #+ then the corresponding process exists.
67 echo "Process #$1 invoked by $exe_file."
68 else
69 echo "No such process running."
70 fi
71
72
73 # This elaborate script can *almost* be replaced by
74 # ps ax | grep $1 | awk '{ print $5 }'
75 # However, this will not work...
76 #+ because the fifth field of 'ps' is argv[0] of the process,
77 #+ not the executable file path.
78 #
79 # However, either of the following would work.
80 # find /proc/$1/exe -printf '%l\n'
81 # lsof -aFn -p $1 -d txt | sed -ne 's/
n//p'
82
83 # Additional commentary by Stephane Chazelas.
84
85 exit 0 |
Example 27-3. On-line connect status
1 #!/bin/bash
2
3 PROCNAME=pppd # ppp daemon
4 PROCFILENAME=status # Where to look.
5 NOTCONNECTED=65
6 INTERVAL=2 # Update every 2 seconds.
7
8 pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME | awk '{ print $1 }' )
9 # Finding the process number of 'pppd', the 'ppp daemon'.
10 # Have to filter out the process lines generated by the search itself.
11 #
12 # However, as Oleg Philon points out,
13 #+ this could have been considerably simplified by using "pidof".
14 # pidno=$( pidof $PROCNAME )
15 #
16 # Moral of the story:
17 #+ When a command sequence gets too complex, look for a shortcut.
18
19
20 if [ -z "$pidno" ] # If no pid, then process is not running.
21 then
22 echo "Not connected."
23 exit $NOTCONNECTED
24 else
25 echo "Connected."; echo
26 fi
27
28 while [ true ] # Endless loop, script can be improved here.
29 do
30
31 if [ ! -e "/proc/$pidno/$PROCFILENAME" ]
32 # While process running, then "status" file exists.
33 then
34 echo "Disconnected."
35 exit $NOTCONNECTED
36 fi
37
38 netstat -s | grep "packets received" # Get some connect statistics.
39 netstat -s | grep "packets delivered"
40
41
42 sleep $INTERVAL
43 echo; echo
44
45 done
46
47 exit 0
48
49 # As it stands, this script must be terminated with a Control-C.
50
51 # Exercises:
52 # ---------
53 # Improve the script so it exits on a "q" keystroke.
54 # Make the script more user-friendly in other ways. |
 |
In general, it is dangerous to write to the files in /proc, as this can corrupt the filesystem or crash the machine. |