LFCS Commands

Commands needed for Linux Foundation Certified Sysadmin.

Processes #

ulimit #

• man page
• get/set the resource limits of processes
• restrict: processes can’t exhaust the system’s resource
• expand: set enough resource to run a propgram properly
• hard limit: the possible maximum of resource, set by root
• soft limit: the possible maximum of resource for user, can’t exceed hard limit
• users and root has different limits
• the settings are valid for the current shell, to modify persistent, write to /etc/security/limits.conf
• get all limit: ulimit -a
• set the limit of open files: ulimit -n 2048

ps #

• man page
• show current processes
• list all processes: ps -elf or ps -aux

nice #

• man page
• set the starting process priority level
• higher nice level means lower priority
• range: -20 to 19
• run a script with lower priority: nice -n 10 ./script or nice -10 ./script
• run a script with higher priority: nice -n -10 ./script or nice --10 ./script

renice #

• man page
• set an already runnning process priority level
• increase a PID’s priority level: renice -n 10 2000 or renice +10 2000
• lower a PID’s priorty level: renice -n -10 2000 or renice -10 2000

ldd #

• man page
• list the shared libraries needed to a binary
• list the shared libraries need by ls: ldd /bin/ls

ldconfig #

• man page
• generally runs at boot time
• used to build a cached database of shared libraries

ipcs #

• man page
• get informations about IPC facilities
• to list facilities with PID: ipcs -p

Signals #

kill #

• man page
• send a signal to a process
• list signals: kill -l
• SIGTERM is the default signal, if the number omitted
• only accept PID!
• kill process using number: kill -n 9 2000 or kill -9 2000
• kill process using name: kill -s SIGKILL 2000 or kill -SIGKILL 2000

killall #

• man page
• kill all processes (those that the caller user can kill) with the given name
• the default signal is SIGTERM
• kill every firefox instance with number: killall -9 firefox
• kill every firefox instance with name: killall -SIGKILL firefox

pkill #

• man page
• send signal to a process with a criteria
• kill very firefox instance of user g0rbe: pkill -u g0rbe firefox