===== Linux okosságok =====

==== Dátum figyelés ====

  function date_diff()
  {
    date='2020-08-12T16:00:10'
    epoch=$(date -d "$date" +%s)
    if [ "$epoch" -lt "$(date -d '1 minute ago' +%s)" ] ; then
  #[[ "$(date -d '2024-02-01 17:26:00' +%s)" -lt "$(date +%s)" ]] && echo elmult || echo nem
        echo At least 3 days ago
    else
        echo Too recent
    fi
  }


==== Reboot, ha nem megy a szabályos reboot ====

  # echo s > /proc/sysrq-trigger
  # echo u > /proc/sysrq-trigger
  # echo s > /proc/sysrq-trigger
  # echo b > /proc/sysrq-trigger

This requests the kernel to do:

emergency sync of the block devices; 
mount readonly of all filesystems; 
again a sync; 
force an immediate boot; (you can also use o for poweroff)

==== dm-* device-ok felderítése ====

  find /dev/ -name "dm-*" -exec readlink -n {} \; -exec echo " -->" {} \;
==== SCSI (re)scan ====

  #!/bin/sh
  for I in `ls -d /sys/class/scsi_device/*`; do
        echo ${I}
        echo "1" > ${I}/device/rescan
  done

  #!/bin/sh
  for I in `ls -d /sys/class/scsi_host/host*`; do
        echo ${I}
        echo "- - -" > ${I}/scan
  done


==== Yum-mal telepített csomagok listázása log fájlból ====

  cat /var/log/yum.log | sed "s#.\+: \?\(.\+\)#\1#" | sort
==== Disk perf. teszt DD-vel ====

<file>
#!/bin/bash
echo -n "Fajl nev: "
read FNEV
echo -n "Blokk meret (Byte): "
read BS
echo -n "Fajl meret (MByte): "
read FS
COUNT=$((FS*1024*1024 / $BS))
COUNT=$(echo $COUNT | sed 's/\..*$/g/')
echo -n "Diszk irasa (dd if=/dev/zero of=$FNEV bs=$BS count=$COUNT)… "
SEC=$(timex dd if=/dev/zero of=$FNEV bs=$BS count=$COUNT 2>&1 | awk '/real/{print $2}' | awk -F'.' '{print $1}')
echo "$(($FS / $SEC)) MB/s"
</file>

==== BOOT probléma ====

GRUB menüben a "quiet" paraméter helyére "dracut rdshell"-t betenni

==== ~/.vimrc ====

  set number background=dark
  syntax on
  highlight Comment    ctermfg=119
  highlight Identifier ctermfg=99AA00
  set ts=4 sw=4
  undolevels=1000
==== RAID megoldások ====

  * Standard RAID: [[http://en.wikipedia.org/wiki/Mdadm|mdadm]]
  * RAID1 TCP-n: [[linux:DRBD|DRBD (Distributed Replicated Block Device)]]
  * RAID1 fájlrendszer szinten: [[http://www.furquim.org/chironfs/index.en.html|ChironFS]]

==== MYSQL mentés ====

Mentés (/etc/mysql/debian.cnf is kell a jelszó miatt):

  mysqldump -u root -ptitok --single-transaction --opt --all-databases -R

Visszaállítás:
  
  mysql -u root -ptitok -B adatbazis < mentes.sql

  
==== LVM snapshot készítés ====

  lvdisplay -C -olv_name,lv_path --noheadings
  lvcreate -s -L 1G -n blabla /dev/vg/blablalv
  lvdisplay -C -S lv_role=snapshot

==== sudo jog másik userhez ====

  non-root-user ALL = (appuser) NOPASSWD: ALL


==== NMON adatgyűjtés ====

<file>
#!/bin/sh

if [ $? -ne 0 ]; then exit 1; fi
ps -ef | grep '[n]mon ' | awk '{print $2}' | while read PID; do kill $PID; done
find /tmp/nmon/$(hostname)_* -type f -maxdepth 1 -mtime +30 -exec rm -f {} \;
# vagy betomoritve:
# find /tmp/nmon/$(hostname)_* -type f -maxdepth 1 -mtime +30 -print0 | xargs -0 tar zcvf $(hostname)_blabla.tar.gz

# Mintaveteli periodus (masodperc)
INTERVAL=60
# Meres idotartama (ora)
DURA=24

SAMPLES=`expr $DURA \* 3600 / $INTERVAL`
cd /tmp/nmon
nmon -f -s $INTERVAL -c $SAMPLES
</file>

==== Email címek extraktálása AIX alatt ====

  perl -wne'while(/[\w\.\-]+@[\w\.\-]+\w+/g){print "$&\n"}'

==== Hiányzik az "add-apt-repository": ====

  sudo apt-get install --reinstall python-software-properties && sudo dpkg-reconfigure python-software-properties

==== Java install: ====

  sudo add-apt-repository ppa:webupd8team/java
  sudo apt-get update
  sudo apt-get install oracle-java7-installer
  java -version
  
==== Mennyi helyet foglal egy bizonyos fájl csoport? ====

  find / -name "*\.trc" -print0 | du --files0-from=- -hc | tail -n1
  
==== Milyen felbontásokat támogat a webcam? ====

  $ lsusb
    Bus 001 Device 002: ID 5986:0241 Acer, Inc BisonCam, NB Pro
  $ lsusb -s 001:002 -v | egrep "Width|Height"
    wWidth    640
    wHeight   480
    wWidth    1280
    wHeight   1024
  ...

==== Helyhasználat listázása fájlrendszerben userenként ====

  find / -printf '%u %k\n' | awk '{arr[$1]+=$2} END {for (i in arr) {print i,arr[i]}}'
  
==== SWAP használat listázása processzenként ====

<file>
#!/bin/bash
# Get current swap usage for all running processes
# Erik Ljungstrom 27/05/2011
echo "Swappiness: $(cat /proc/sys/vm/swappiness)"
SUM=0
OVERALL=0
for DIR in `find /proc/ -maxdepth 1 -type d | egrep "^/proc/[0-9]"` ; do
PID=`echo $DIR | cut -d / -f 3`
PROGNAME=`ps -p $PID -o comm --no-headers`
for SWAP in `grep Swap $DIR/smaps 2>/dev/null| awk '{ print $2 }'`
do
let SUM=$SUM+$SWAP
done
echo "PID=$PID - Swap used: $SUM - ($PROGNAME )"
let OVERALL=$OVERALL+$SUM
SUM=0
done
echo "Overall swap used: $OVERALL"
</file>

==== Törölt fájlok, amik nem szabadították még fel a helyet ====
  lsof |(sed 1q; grep deleted)
    
==== Hosszú processz végeztéről értesítő email ====

<file>
#!/bin/bash
MAILTO="rvenyige@pcs.hu,pagoston@pcs.hu"
SSH="ssh -i /home/pagoston/.ssh/id_rsa pagoston@sapeltora "
while [ $($SSH "ps -ef | awk '{print $2}'" | grep -c "$1") -gt 0 ]; do
        sleep 60
done
echo Lefutott | mail -s "Process $1 lefutott (${hostname})" $MAILTO
</file>

==== processz elrejtése a PS kimenetből ====


<file>
/* https://unix.stackexchange.com/a/403918/119298
 * capture calls to a routine and replace with your code
 * gcc -Wall -O2 -fpic -shared -ldl -o shim_main.so shim_main.c
 * LD_PRELOAD=/.../shim_main.so theprogram theargs...
 */
#define _GNU_SOURCE /* needed to get RTLD_NEXT defined in dlfcn.h */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <dlfcn.h>

typedef int (*pfi)(int, char **, char **);
static pfi real_main;

/* copy argv to new location */
char **copyargs(int argc, char** argv){
    char **newargv = malloc((argc+1)*sizeof(*argv));
    char *from,*to;
    int i,len;

    for(i = 0; i<argc; i++){
        from = argv[i];
        len = strlen(from)+1;
        to = malloc(len);
        memcpy(to,from,len);
        memset(from,'\0',len);    /* zap old argv space */
        newargv[i] = to;
        argv[i] = 0;
    }
    newargv[argc] = 0;
    return newargv;
}

static int mymain(int argc, char** argv, char** env) {
    fprintf(stderr, "main argc %d\n", argc);
    return real_main(argc, copyargs(argc,argv), env);
}

int __libc_start_main(pfi main, int argc,
                      char **ubp_av, void (*init) (void),
                      void (*fini)(void),
                      void (*rtld_fini)(void), void (*stack_end)){
    static int (*real___libc_start_main)() = NULL;

    if (!real___libc_start_main) {
        char *error;
        real___libc_start_main = dlsym(RTLD_NEXT, "__libc_start_main");
        if ((error = dlerror()) != NULL) {
            fprintf(stderr, "%s\n", error);
            exit(1);
        }
    }
    real_main = main;
    return real___libc_start_main(mymain, argc, ubp_av, init, fini,
            rtld_fini, stack_end);
}
</file>

==== Hasznos oldalak ====

  * [[http://tsm.agostonpeter.com/letix.html|Linux parancsok, kezdőknek (www.letix.hu)]]
  * [[http://tldp.fsf.hu/HOWTO/sag-hu/index.html|Linux rendszeradminisztrátorok kézikönyve]]
  * [[http://linuxconfig.org/bash-scripting-tutorial|Bash scripting Tutorial]]
  * [[http://sed.sourceforge.net/sed1line.txt|Handy one-liners for SED]]
  * [[http://www.grymoire.com/Unix/Sed.html|Sed - An Introduction and Tutorial by Bruce Barnett]]
  * [[http://tldp.org/LDP/abs/html/index.html|Advanced Bash-Scripting Guide]]
  * [[http://gsteph.blogspot.hu/2007/04/bash-reading-text-file.html|BASH: Reading Text File]]
  * [[http://www.howtogeek.com/howto/ubuntu/keyboard-shortcuts-for-bash-command-shell-for-ubuntu-debian-suse-redhat-linux-etc/|Keyboard Shortcuts for Bash]]
  * [[https://github.com/gdbtek/linux-cookbooks/blob/master/libraries/util.bash|Bash util functions]]
  * [[https://ef.gy/forwarding-ipv4-to-ipv6|Forwarding IPv4 Ports to IPv6-only Hosts]]
  * [[https://www.techrepublic.com/article/how-to-setup-two-factor-authentication-in-linux|Két faktoros authentikáció linuxon]]
  * [[https://access.redhat.com/articles/17054|How do I find the FC ID (WWN) of a scsi device/LUN on Red Hat Enterprise Linux?]]