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. Certain system commands, such as procinfo,
free, vmstat, lsdev, and
uptime do this as well.
FS=iso # ISO filesystem support in kernel?
grep $FS /proc/filesystems # iso9660
Example:
kernel_version=$( awk '{ print $3 }' /proc/version )Example:
CPU=$( awk '/model name/ {print $5}' < /proc/cpuinfo )
if [ "$CPU" = "Pentium(R)" ] then run_some_commands ... else run_other_commands ... fi
cpu_speed=$( fgrep "cpu MHz" /proc/cpuinfo | awk '{print $4}' ) # Current operating speed (in MHz) of the cpu on your machine. # On a laptop this may vary, depending on use of battery #+ or AC power.
Example:
!/bin/bash # get-commandline.sh # Get the command-line parameters of a process.
OPTION=cmdline
# Identify PID. pid=$( echo $(pidof "$1") | awk '{ print $1 }' ) # Get only first ^^^^^^^^^^^^^^^^^^ of multiple instances.
echo echo "Process ID of (first instance of) "$1" = $pid" echo -n "Command-line arguments: " cat /proc/"$pid"/"$OPTION" | xargs -0 echo # Formats output: ^^^^^^^^^^^^^^^ # (Thanks, Han Holl, for the fixup!)
echo; echo
# For example: # sh get-commandline.sh xterm
Example:
devfile="/proc/bus/usb/devices" text="Spd" USB1="Spd=12" USB2="Spd=480"
bus_speed=$(fgrep -m 1 "$text" $devfile | awk '{print $9}') # ^^^^ Stop after first match.
if [ "$bus_speed" = "$USB1" ] then echo "USB 1.1 port found." # Do something appropriate for USB 1.1. fi
Note: It is even possible to control certain peripherals with commands
sent to the /proc directory.
root# echo on > /proc/acpi/ibm/light
This turns on the Thinklight in certain models of IBM/Lenovo Thinkpads. (May not work on all Linux distros.)
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.
Finding the process associated with a PID
#!/bin/bash # pid-identifier.sh: # Gives complete path name to process associated with pid.
ARGNO=1 # Number of arguments the script expects. E_WRONGARGS=65 E_BADPID=66 E_NOSUCHPROCESS=67 E_NOPERMISSION=68 PROCFILE=exe
if [ $# -ne $ARGNO ] then echo "Usage: `basename $0` PID-number" >&2 # Error message >stderr. exit $E_WRONGARGS fi
pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 ) # Checks for pid in "ps" listing, field #1. # Then makes sure it is the actual process, not the process invoked by this script. # The last "grep $1" filters out this possibility. # # pidno=$( ps ax | awk '{ print $1 }' | grep $1 ) # also works, as Teemu Huovila, points out.
if [ -z "$pidno" ] # If, after all the filtering, the result is a zero-length string, then #+ no running process corresponds to the pid given. echo "No such process running." exit $E_NOSUCHPROCESS fi
# Alternatively: # if ! ps $1 > /dev/null 2>&1 # then # no running process corresponds to the pid given. # echo "No such process running." # exit $E_NOSUCHPROCESS # fi
# To simplify the entire process, use "pidof".
if [ ! -r "/proc/$1/$PROCFILE" ] # Check for read permission. then echo "Process $1 running, but..." echo "Can't get read permission on /proc/$1/$PROCFILE." exit $E_NOPERMISSION # Ordinary user can't access some files in /proc. fi
# The last two tests may be replaced by: # if ! kill -0 $1 > /dev/null 2>&1 # '0' is not a signal, but # this will test whether it is possible # to send a signal to the process. # then echo "PID doesn't exist or you're not its owner" >&2 # exit $E_BADPID # fi
exe_file=$( ls -l /proc/$1 | grep "exe" | awk '{ print $11 }' ) # Or exe_file=$( ls -l /proc/$1/exe | awk '{print $11}' ) # # /proc/pid-number/exe is a symbolic link #+ to the complete path name of the invoking process.
if [ -e "$exe_file" ] # If /proc/pid-number/exe exists, then #+ then the corresponding process exists. echo "Process #$1 invoked by $exe_file." else echo "No such process running." fi
# This elaborate script can *almost* be replaced by # ps ax | grep $1 | awk '{ print $5 }' # However, this will not work... #+ because the fifth field of 'ps' is argv[0] of the process, #+ not the executable file path. # # However, either of the following would work. # find /proc/$1/exe -printf '%l\n' # lsof -aFn -p $1 -d txt | sed -ne 's/^n//p'
# Additional commentary by Stephane Chazelas.
exit 0
On-line connect status
#!/bin/bash # connect-stat.sh # Note that this script may need modification #+ to work with a wireless connection.
PROCNAME=pppd # ppp daemon PROCFILENAME=status # Where to look. NOTCONNECTED=85 INTERVAL=2 # Update every 2 seconds.
pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME | awk '{ print $1 }' )
# Finding the process number of 'pppd', the 'ppp daemon'. # Have to filter out the process lines generated by the search itself. # # However, as Oleg Philon points out, #+ this could have been considerably simplified by using "pidof". # pidno=$( pidof $PROCNAME ) # # Moral of the story: #+ When a command sequence gets too complex, look for a shortcut.
if [ -z "$pidno" ] # If no pid, then process is not running. then echo "Not connected." # exit $NOTCONNECTED else echo "Connected."; echo fi
while [ true ] # Endless loop, script can be improved here. do
if [ ! -e "/proc/$pidno/$PROCFILENAME" ] # While process running, then "status" file exists. then echo "Disconnected." # exit $NOTCONNECTED fi
netstat -s | grep "packets received" # Get some connect statistics. netstat -s | grep "packets delivered"
sleep $INTERVAL echo; echo
done
exit 0
# As it stands, this script must be terminated with a Control-C.
# Exercises: # --------- # Improve the script so it exits on a "q" keystroke. # Make the script more user-friendly in other ways. # Fix the script to work with wireless/DSL connections.
Warning: In general, it is dangerous to write to the files in
/proc, as this can corrupt the filesystem or crash the
machine.