Root and Administrator Tasks: Process Management

• UNIX root privileged accounts
• If a process has a userid of 0, many restrictions such as permission checks from processes are not enforced (unless you are running SELinux.) These are generally called root processes; root processes can, tattoueba:

Root and Administrator Tasks: Process Management

• Mount and unmount file systems -- however, that's not quite true on Linux machines; the mount(8) program is now being suid to root on some (many) distributions.

Root and Administrator Tasks: Process Management

If the keyword user is specified in a mount point defined in /etc/fstab, then many newer versions of the mount program will allow a user to mount or unmount that specific filesystem. (This is becoming a very smooth process in many distributions, and plugging in/removing a USB drive is now usually pleasant experience. While there is much flux here, some distributions are giving unique names such as the UUID name as part of the mount name.)

UUID=a34a9b1e-82f6-4d91-a407-f5a769ed09b8 /                       ext4    defaults        1 1
UUID=4d9116c5-2316-4f3c-85fb-63e676f2b500 /boot                   ext4    defaults        1 2
UUID=577175b5-e86f-4960-be80-995ae53fee68 /home                   ext4    defaults        1 2
UUID=f871903f-2399-4777-9879-17bbf05f9aa2 swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
UUID=9efcbabb-7914-4652-a92f-1a4683e57b32 /mnt1  ext3 defaults 0 0
UUID=0d2b19ef-e426-4cea-af91-06f3bdef580b /mnt2  ext3 defaults 0 0

      

Root and Administrator Tasks: Process Management

• Root processes can set a process's filesystem root to a subdirectory of a filesystem via chroot(2)
• Create device files (/dev, mknod)
• Set the system clock
• Can access any local file

Root and Administrator Tasks: Process Management

• Change file ownership
• Raise resource limits (datasize, stacksize, coresize) -- no other userid than 0 can do so; other userids can only lower resources limits
• Lower nice values (raising priority)

Root and Administrator Tasks: Process Management

• Change system's hostname
• Run halt, shutdown, telinit
• Manage print subsystems

Root and Administrator Limitations: Process Management

• Many other programs check to see if the current process is running under uid 0 (the code to check for this usually looks something like if geteuid() == 0) {...})

Root and Administrator Limitations: Process Management

• What limitations and restrictions are there to such root processes?
• UNIX suffers from ``userid 0 has all powers'', so root account (and its password(s)) are a strong focal point for security breakins, either directly or via privilege escalation once control of an ordinary process is effected.

Privilege escalation for the privileged

• How to become ``root''? Generally, people use something along the way of sudo, su, or login
• Ancient caveats: The login program still enforces criteria about using an ``allowed'' terminal (in /etc/ttytab (BSD), /etc/default/login (Solaris) or /etc/securetty (RedHat Linux, Debian).)

How does a human "user" become root? login, su, sudo

• Execute the su command
• su = Substitute User

How to become root? login, su, sudo

• su with minus flag (su - fc5) invokes a ``login'' session
• Good idea to su - root. The advantages of a ``login'' shell:
• Paths are those of root, not your current processes

How to become root? login, su, sudo

• Set up items such as ``safe'' aliases for dangerous programs such as
• rm → rm -i
• cp → cp -i
• mv → mv -i

sudo: pseudo su, or how to set up safer su

• Ubuntu tries to make it universal, others also
• Allows a class of users to execute a set of commands with root privileges (the configuration is flexible enough to do lots more)

sudo: pseudo su, or how to set up safer su

• Logs the use of the ``sudo'' command (but does not log the commands executed by the shells that are started by sudo !)
• Does raise some vulnerabilities since it is yet-another setuid program (YASUP?)

sudo: pseudo su, or how to set up safer su

# sudoers file.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# Host alias specification

# User alias specification

sudo: pseudo su, or how to set up safer su

# Cmnd alias specification

# Defaults specification

# User privilege specification
root	ALL=(ALL) ALL

# Uncomment to allow people in group wheel to run all commands
# %wheel	ALL=(ALL)	ALL

sudo: pseudo su, or how to set up safer su

# Same thing without a password
# %wheel	ALL=(ALL)	NOPASSWD: ALL

# Samples
# %users  ALL=/sbin/mount /cdrom,/sbin/umount /cdrom
# %users  localhost=/sbin/shutdown -h now

user1	monet=/usr/local/bin/suroot, /bin/su

System Load Average

``load average'' == average size of ready queue over sample period

• Shows the 1, 5, and 15 minute load averages
• Can see with w, uptime, or top

System Load Average

• What's a reasonable load average? → depends on the machine and the type of jobs running
• When I wrote these notes, I was using a computer with quad-core and 4 gigabytes of memory; it also had two processes crunching numbers and a load average over 2, but it's not loaded and is very responsive.

Idle Time

• Percentage of time the system is idle
• Can see with dstat , iostat -c 1, top, or vmstat 1
• What do you want this number to be? (again, it depends on machine's raison d'etre)

Idle Time

iostat -c 1
Linux 2.6.27.24-170.2.68.fc10.x86_64 (localhost.localdomain) 	06/11/2009

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          57.04    0.20    0.97    0.07    0.00   41.73

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          50.50    0.00    0.00    0.99    0.00   48.51

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          51.36    0.00    0.25    0.00    0.00   48.39

Process Monitoring: ps

• ps comes from process status; LAH has comprehensive information
• Shows a window into process table via the filesystem -- remember, ps these days generally is just walk through the /proc pseudo-filesystem

Process Monitoring: ps

• Rich command options set; unfortunately, there are different options depending on whether the OS is BSD or System V based.

Process Manipulation:

As a system administrator, you can adjust the priority of a process with renice:

renice +19 PID    ##  lowest priority (nice)
renice -19 PID    ## highest priority (not nice)

Example ps output from long, long ago

USER       PID %CPU %MEM   SZ  RSS TT STAT START   TIME COMMAND
-----------------------------------------------------------------------
kuncick   7467 40.1 1.3   124  364 pc D <  09:32   0:15 find / -name foo
kuncick   7419 16.6 1.3   124  364 pc D N  09:28   0:11 find ... 
kuncick   7529 39.4 1.2   100  320 pc R    09:35   0:01 find / -name foo 
kuncick   7528 35.8 1.2   112  324 pc R    09:35   0:15 find / -name foo 
root         1  0.0 0.0    52    0 ?  IW   Dec 18  0:24 /sbin/init - 
root         2  0.0 0.0     0    0 ?  D    Dec 18  0:08 pagedaemon 
root        75  0.0 0.4    48  108 ?  S    Dec 18 12:09 in.routed 
bynum     7328  0.0 0.1    48   24 pb S    09:24   0:00 rlogin

Example ps output from the more recent past

F   UID   PID  PPID PRI  NI   VSZ  RSS WCHAN  STAT TTY        TIME COMMAND
--------------------------------------------------------------------------
5     0  1778     1  24   0  1528  512 -      S    ?          0:00 /usr/sbin/apmd -p
 10 -w 5 -W -P /etc/sysconfig/apm-scripts/apmscript
5     0  1866     1  15   0  2144  880 -      S    ?          0:00 xinetd -stayalive
 -pidfile /var/run/xinetd.pid
1    51  1902     1  15   0  5992 2284 -      S    ?          0:00 sendmail: Queue
 runner@00:01:00 for /var/spool/clientmqueue
1    49  1949     1  25   0  5296 4012 -      S    ?          0:00 /usr/bin/jserver

Example ps output from the more recent past

4   500  2089  2068  15   0 18364 8948 schedu S    ?          0:00 /usr/bin/gnome-session 
SSH_AGENT_PID=2140 HOSTNAME=sophie.cs.fsu.edu TERM=dumb SHELL=/bin/bash HISTSIZE=1000 
QTDIR=/usr/lib/qt-3.1 USER=langley LS_COLORS= SSH_AUTH_SOCK=/tmp/ssh-sQIL2089/agent.2089 
PATH=/usr/kerberos/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/home/langley/bin 
MAIL=/var/spool/mail/langley PWD=/home/langley INPUTRC=/etc/inputrc XMODIFIERS=@im=none 
LANG=en_US.UTF-8 LAMHELPFILE=/etc/lam/lam-helpfile GDMSESSION=Default 
SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass SHLVL=1 HOME=/home/langley 
LOGNAME=langley LESSOPEN=|/usr/bin/lesspipe.sh %s DISPLAY=:0 G_BROKEN_FILENAMES=1 
XAUTHORITY=/home/langley/.Xauthority
0     0  7601  7365  15   0 11320 5528 -      S    pts/1      0:00 emacs -nw

Many more features to ps

• Note that ps causes the ``observer effect'' (observing the process table affects the process table, which is very true of top, especially if you set it to rapidly refresh)

Many more features to ps

Some favorite ps variations:

• ps -ef(System V)
• ps -elf (System V)
• ps axuw | grep username (BSD)
• ps alxwww (BSD)
• ps alxwwwe (BSD, show environmental variables)

ps itself can also act a bit like pstree

$ ps f
  PID TTY      STAT   TIME COMMAND
21915 pts/1    Ss     0:00 bash
22976 pts/1    S+     0:05  \_ emacs -nw 05-rootadmins.tex
27844 pts/2    Ss     0:00      \_ /bin/bash --noediting -i
17182 pts/2    R+     0:00          \_ ps f
18985 pts/0    Ss     0:00 bash
19153 pts/0    S+     0:00  \_ ssh langley@diablo.cs.fsu.edu

Making ps ultra-flexible

If you need to tailor ps output to arbitrary columns, you can use the -o option to specify exactly which columns you would like to display, and -k option to specify order:

$ ps k pid o pid,comm
  PID COMMAND
18985 bash
19153 ssh
21915 bash
22976 emacs
24527 ps
27844 bash

Making ps ultra-flexible

$ ps k comm o pid,comm
  PID COMMAND
18985 bash
21915 bash
27844 bash
22976 emacs
24729 ps
19153 ssh

Other process viewing tools

• top -- Dynamically shows processes, idle time, memory usage, and load averages
• pstree -- Nice filter that shows family hierarchy of processes

top example

[root@smtpin MailScanner]# top -b -n 1
top - 07:09:25 up 42 days, 20:18,  2 users,  load average: 1.34, 1.56, 1.79
Tasks: 166 total,   1 running, 165 sleeping,   0 stopped,   0 zombie
Cpu(s): 12.7% us,  1.6% sy,  0.0% ni, 84.3% id,  1.3% wa,  0.0% hi,  0.0% si
Mem:   4149124k total,  3794188k used,   354936k free,   202476k buffers
Swap:  4192956k total,     4960k used,  4187996k free,  2677940k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 5675 root      15   0 68888  58m 2788 S    4  1.4   0:03.08 MailScanner
 5686 root      15   0  3520  900  676 R    2  0.0   0:00.01 top
26663 root      16   0 38616  29m 3464 S    2  0.7   0:29.90 MailScanner
    1 root      16   0  1980  548  468 S    0  0.0   0:45.81 init

pstree example

init-+-MailScanner
     |-MailScanner-+-16*[MailScanner]
     |             `-4*[MailScanner---MailScanner]
     +-acpid
     +-atd
     +-clamd
     +-crond
     +-cups-config-dae
     +-cupsd

Root remedies for sluggish system

System clogged by many identical jobs → restarting and limiting

Real world example:

You log into a mail server and find a high load 
average, and many, many sendmail processes running 
on the machine. Doing an mailq reveals that 
there are many, many undelivered messages. It turns that out the network that 
this machine normally uses to send mail out was down for a few hours and a lot
of mail has accumulated.

Root remedies for sluggish system

This system should have its queues cleared. To do this efficiently, you decide to stop further incoming mail until you have cleared out the older, undelivered email. You can stop sendmail with something like:

/etc/init.d/sendmail stop

Root remedies for sluggish system

However, that only stops sendmail.

You now need to clear some of the queue. One way to do this is with the -qf option:

/usr/sbin/sendmail -qf -v

Root remedies for sluggish system

This leaves this new sendmail process running in the 
foreground just as a queue handler, running 
``verbosely'' so that you can see exactly what it is 
doing, and how long it is taking. 

Root remedies for sluggish system

Starting a few of these foreground queue handlers will allow the queues 
to clear more quickly than if you just turn on the 
regular incoming email and a single background
queue handler.

Root root remedies for sluggish system

Another example:

One process has been running for a long time and is 
accumulating a lot of processor time (for instance, top
shows it at the top of the list consistently) → typically,
this can be cleaned up by simply killing that one process. (If this is an
ordinary user process, this is
often the result of a controlling terminal having gone awry.)

Root remedies for sluggish system

• Long-term Remedies
• Involve more performance analysis (for instance, you might try the venerable SAR package to profile a Linux/Unix system; in the Windows world, Microsoft has LOGMAN and PAL; you can use tools like "dstat", "perf top", and "perf stat")
• More physical resources are inexpensive: may need more nodes, nodes may need faster CPU, more memory, better i/o

Root remedies for sluggish system

• Finally: talk to people writing code; often small optimizations in database access, for instance, can have large performance gains

Windows Administrator Powers

• The Windows administrator account has also suffered somewhat from the UNIX ``one account has all powers'' model.

Windows Administrator Powers

• Windows ``powers'' are defined as a set of user rights policies, assigned either individually to an account or via group memberships. The rights are:
• Access this computer from network
• Add workstations to domain
• Back up files and directories

Windows Administrator Powers

• Change the system time
• Force shutdown from a remote system
• Load and unload device drivers
• Log on locally

Windows Administrator Powers

• Manage auditing and security log
• Restore files and directories
• Shut down the system
• Take ownership of files or other objects

Windows Administrator Powers

• Windows also provides a set of advanced user rights, mostly for software developers.
• Bypass traverse checking (ignore directory perms)
• Act as part of the operating system (system-level access)

Windows Administrator Powers

• Increase scheduling priorities
• Lock pages in memory
• Profile system performance

The future?

Administrators, by definition, have much more access to systems than ordinary users — this came into the public's consciousness most strongly recently with the Snowden situation

Permissions have not generally been enforced for privileged processes. However, with systems such as SeLinux and TOMOYO, we are now seeing enforcement of security policies even for privileged processes -- this can be disconcerting to system administrators who are used to privileged processes having free rein.