linux_admin

PninoH

1.Monitoring the system
pstree  Processes and parent-child relationships
top     Show top processes
iostat  Report CPU statistics and input/output statistics for devices and partitions.
ps -auxw  process status
uname -a  print system information
cat /proc/version  Display Linux kernel version in use.
cat /etc/redhat-release  Display Red Hat Linux Release. (also /etc/issue)
uptime  Tell how long the system has been running. Also number of users and system's load average.
w  Show who is logged on and what they are doing.
/sbin/lsmod  List all currently loaded kernel modules.
Same as cat /proc/modules
/sbin/runlevel  Displays the system's current runlevel.
hostname  Displays/changes the system's node name. (Must also manually change hostname setting in /etc/sysconfig/network. Command will change entry in /etc/hosts)
service Red Hat/Fedora command to display status of system services.
Example: service --status-all
Help: service --help

2.Memory Usage
vmstat  Monitor virtual memory
free  Display amount of free and used memory in the system. (Also: cat /proc/meminfo)
pmap  Display/examine memory map and libraries (so). Usage: pmap pid
top  Show top processes
sar -B Show statistics on page swapping.
time -v date  Show system page size, page faults, etc of a process during execution. Note you must fully qualify the command as "/usr/bin/time" to avoid using the bash shell command "time".
cat /proc/sys/vm/freepages Display virtual memory "free pages".
One may increase/decrease this limit: echo 300 400 500 > /proc/sys/vm/freepages
cat /proc/meminfo  Show memory size and usage.
3.User Info:
Commands:
who  Displays currently logged in users.
Use who -uH for idle time and terminal info.
users  Show all users logged in.  
w  Displays currently logged in users and processes they are running.  
whoami  Displays user id.
groups  Display groups you are part of.
Use groups user-id to display groups for a given user.  
set  Display all environment variables in your current environment.  
id  Display user and all group ids.
Use id user-id to display info for another user id.
last  Listing of most recent logins by users. Show where from, date and time of login (ftp, ssh, ...) Also see lastlog command.
Show last 100 logins: last -100
history  Shell command to display previously entered commands.  


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