Linux notes

Posted by Ravikiran K.S. on January 1, 2006

Linux tips n tricks

service command

list running services $ service –status-all

Print the status of any service $ service httpd status

List all known services (configured via SysV) $ chkconfig –list

Turn on/off service $ ntsysv $ chkconfig service off Ex. chkconfig httpd off $ chkconfig service on Ex. chkconfig ntpd on

Which package or RPM does this file belongs to?

$ rpm -q -f /usr/bin/hexdump

Reboot machine when everything is hanging

<alt> + <print screen/sys rq> + <R> - <S> - <E> - <I> - <U> - <B>

Get page size under Linux

$ getconf PAGESIZE or getconf PAGE_SIZE

simple python smtp server

$ python -m smtpd -n -c DebuggingServer localhost:1025

To check given package existance on Ubuntu

$ dpkg –get-selections | grep php

To list all binaries belonging to a package on Ubuntu

$ dpkg -L php5-gd

APR indent style options for ‘indent’ command (in indent.pro file)

-i4 -npsl -di0 -br -nce -d0 -cli0 -npcs -nfc1 -nut

A very simple and useful stopwatch

$ time read (ctrl-d to stop)

Summarize a patch file

$ cat patches.log | grep “Patch:” | cut -c 1-16 > patches.log.small

When some output is piped through ‘less’, it can be saved before exiting by pressing ‘s’.

Match both process name and argument list for process being searched.

Similarly, prints a verbose output $ pgrep -lf screen

$ find /home -xdev -samefile file1 | xargs rm $ find /home -xdev -inum 2655341

Replace a file with new file while not loosing original file attributes

This is useful for cases, where you would like to do replace while preserving the date & time of original file $ cp –attributes-only file file.tmp $ cp -l -b -f file file $ $filter < file > file.tmp && $ mv file.tmp file

  1. stat - display file or filesystem status [root@xe30-1][~]$ stat rkks/.bashrc File: `rkks/.bashrc’ Size: 124 Blocks: 8 IO Block: 4096 regular file Device: 802h/2050d Inode: 220095 Links: 1 Access: (0644/-rw-r–r–) Uid: ( 20/ rkks) Gid: ( 0/ root) Access: 2008-03-11 12:25:59.000000000 +0530 Modify: 2008-03-11 12:24:43.000000000 +0530 Change: 2008-03-11 12:24:43.000000000 +0530

  2. pmap - report memory map of a process
  3. pmap_dump - print a list of all registered RPC programs
  4. pmap_set - set the list of registered RPC programs
  5. pgrep, pkill - look up or signal processes based on name and other attributes
  6. pstree - display a tree of processes
  7. pstack - print a stack trace of a running process
  8. nm - list symbols from object files
  9. ptrace - process trace
  10. strace - trace system calls and signals
  11. top - display Linux tasks
  12. ltrace - A library call trace
  13. free - Display amount of free and used memory in the system (also see ‘/proc/meminfo’)
  14. uptime - Tell how long the system has been running.
  15. slabtop - display kernel slab cache information in real time
  16. vmstat - Report virtual memory statistics (also see /proc/stat or /proc/*/stat)
  17. w - Show who is logged on and what they are doing.
  18. iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.
  19. sar - Collect, report, or save system activity information.
  20. mpstat - Report processors related statistics.
  21. utmp
  22. sa1 - Collect and store binary data in the system activity daily data file.
  23. sa2 - Write a daily report in the /var/log/sa directory.
  24. fuser - identify processes using files or sockets
  25. lsof - list open files
  26. access - determine whether a file can be accessed
  27. crash - Analyze Linux crash data or a live system
  28. netdump - send oops data and memory dumps over the network
  29. netstat - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
  30. readlink - display value of a symbolic link
  31. portmap - DARPA port to RPC program number mapper
  32. tcpd - access control facility for internet services
  33. rpcinfo - report RPC information
  34. hosts_access, hosts_ctl, request_init, request_set - access control library
  35. hosts_options - host access control language extensions
  36. xinetd - the extended Internet services daemon
  37. xinetd.conf - Extended Internet Services Daemon configuration file
  38. hardlink - Consolidate duplicate files via hardlinks
  39. strings - print the strings of printable characters in files.
  40. objdump - display information from object files.
  41. readelf - Displays information about ELF files.

  42. readprofile - a tool to read kernel profiling information.