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• Root cannot access /dev/urandom

  - by Darren Newton

  I am trying to generate a GPG key, and I cannot generate enough entropy. So I installed rng-tools and tried following these instructions: http://serverfault.com/questions/214605/gpg-not-enough-entropy When I am logged in as root, and try to run rngd -r /dev/urandom I get the following error: can't open /dev/random: Permission denied I find this disturbing as I am root. This is Ubuntu on a virtual server (via Parallels I believe.)

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• Trim on encrypted SSD--Urandom first?

  - by cb474

  My understanding (I'm not sure I'm getting this all right) is that if one uses Trim on an encrypted SSD, it defeats some of the security benefits, because the drive will write zeros to empty space (as files are deleted). See: http://www.askubuntu.com/questions/115823/trim-on-an-encrypted-ssd And: http://asalor.blogspot.com/2011/08/trim-dm-crypt-problems.html My question is: From the perspective of the performance of the SSD and the functioning of Trim, would it therefore be better to simply zero out the SSD, before setting up an encrypted system, rather than writing random data to the drive, with urandom, as one usually does? Would this basically leave one with the same level of security anyway? And more importantly, would it better enable the Trim functionality to work as intended, with the encrypted SSD?

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• Does urandom share the same entropy of random?

  - by ???

  Does the entropy pool /dev/random used the same to /dev/urandom? I want to mknod /dev/random 1 9 to replace the slow random, I think the current entropy is randomly enough, if urandom is based on the same entropy, and all succeed random numbers are generated based on that entropy, I don't think there'll be any vulnerable.

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• how to show the right word in my code, my code is : os.urandom(64)

  - by zjm1126

  My code is: print os.urandom(64) which outputs: > "D:\Python25\pythonw.exe" "D:\zjm_code\a.py" \xd0\xc8=<\xdbD' \xdf\xf0\xb3>\xfc\xf2\x99\x93 =S\xb2\xcd'\xdbD\x8d\xd0\\xbc{&YkD[\xdd\x8b\xbd\x82\x9e\xad\xd5\x90\x90\xdcD9\xbf9.\xeb\x9b>\xef#n\x84 which isn't readable, so I tried this: print os.urandom(64).decode("utf-8") but then I get: > "D:\Python25\pythonw.exe" "D:\zjm_code\a.py" Traceback (most recent call last): File "D:\zjm_code\a.py", line 17, in <module> print os.urandom(64).decode("utf-8") File "D:\Python25\lib\encodings\utf_8.py", line 16, in decode return codecs.utf_8_decode(input, errors, True) UnicodeDecodeError: 'utf8' codec can't decode bytes in position 0-3: invalid data What should I do to get human-readable output?

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• Is there an alternative to /dev/urandom?

  - by altCognito

  Is there some faster way than /dev/[u]random? Sometimes, I need to do things like cat /dev/urandom /dev/sdb The random devices are "too" secure und unfortunately too slow for that. I know that there are wipe and similar tools for secure deletion, but I suppose there are also some on-board means to that in Linux.

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• Why is /dev/urandom only readable by root since Ubuntu 12.04 and how can I "fix" it?

  - by Joe Hopfgartner

  I used to work with Ubuntu 10.04 templates on a lot of servers. Since changing to 12.04 I have problems that I've now isolated. The /dev/urandom device is only accessible to root. This caused SSL engines, at least in PHP, for example file_get_contents(https://... to fail. It also broke redmine. After a chmod 644 it works fine, but that doesnt stay upon reboot. So my question. why is this? I see no security risk because... i mean.. wanna steal some random data? How can I "fix" it? The servers are isolated and used by only one application, thats why I use openvz. I think about something like a runlevel script or so... but how do I do it efficiently? Maby with dpkg or apt? The same goes vor /dev/shm. in this case i totally understand why its not accessible, but I assume I can "fix" it the same way to fix /dev/urandom

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• How to use /dev/random or urandom in C ?

  - by stojance

  I want to use /dev/random or /dev/urandom in C - how can i do it ? I don't know how can i handle them in C, if someone knows please tell me how. Thank you.

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• Are there any command line utilities which can calculate and/or limit how fast a pipe is running?

  - by stsquad

  I'm doing some basic stress testing of a Linux kernel network IWF with netcat. The set-up is fairly simple. On the target side: nc -l -p 10000 > /dev/null And on my desktop I was running: cat /dev/urandom | nc 192.168.0.20 10000 I'm using urandom for some poor-mans fuzz testing. However I find that even at this rate I can break something quite quickly. EDIT So I've been playing with trickle to rate limit how fast I'm generating data: cat /dev/urandom | trickle -u 10 nc 192.168.0.20 10000 But it's hard to tell if this is working. What would be really useful is a the pv equivilent of trickle that can work with pipes.

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• Simple Python Challenge: Fastest Bitwise XOR on Data Buffers

  - by user213060

  Challenge: Perform a bitwise XOR on two equal sized buffers. The buffers will be required to be the python str type since this is traditionally the type for data buffers in python. Return the resultant value as a str. Do this as fast as possible. The inputs are two 1 megabyte (2**20 byte) strings. The challenge is to substantially beat my inefficient algorithm using python or existing third party python modules (relaxed rules: or create your own module.) Marginal increases are useless. from os import urandom from numpy import frombuffer,bitwise_xor,byte def slow_xor(aa,bb): a=frombuffer(aa,dtype=byte) b=frombuffer(bb,dtype=byte) c=bitwise_xor(a,b) r=c.tostring() return r aa=urandom(2**20) bb=urandom(2**20) def test_it(): for x in xrange(1000): slow_xor(aa,bb)

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• Random password variable disappears

  - by snaken

  Hi, I'm using the following to generate a random password in a shell script: DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) When i run this in a file on its own like this: #!/bin/sh DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) echo $DBPASS A password is echoed. When i incorporate it into a larger script though the variable never seems to get created for some reason, so for example this doesn't work: DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) sed -i s/oldpass/$DBPASS/ mysql_connect.php If i manually set the variable though everything is fine.. can anyone see why?

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• how do you authenticate a user between two services, if they are both using a common third-party oauth service?

  - by urandom

  I'm currently experimenting with oauth logins on a website, using google oauth2. While I set that up without too many problems, I saw that there isn't some kind of permanent token, which only google and the authorized service know about a user. Also, from what I gathered, if I were to create a companion app on android, the preferred way is to go with AccountManager, which seems to handle giving oauth2 access tokens for google accounts. But if I authenticate myself from the anroid app using a google account, how do I now link that user to the same one in the web app? One way I think this can be done if the user also logs into the web app as well, so that the server receives a fresh access token, and the android and web one are compared. But that seems like a huge hassle, and I haven't seen many other apps do that. Another is to use a refresh token on the server, but that would require extra permissions which might put off any potential visitors. So what is the general workflow for achieving this? Or am I thinking the wrong way?

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• cryptsetup partitions not detected at boot

  - by Luis

  I installed a fresh 12.04 and tried to mimic what I had for 10.04. swap should be encrypted with a urandom key and there's another partition that will contain home and other directories. # cat /etc/crypttab | grep -v '^#' | grep -v '^$' cryptswap /dev/sda5 /dev/urandom swap encriptado /dev/sda6 # grep -e 'cryptswap' -e 'encriptado' /etc/fstab /dev/mapper/cryptswap swap swap defaults 0 0 /dev/mapper/encriptado /encriptado ext4 defaults 0 0 I also apt-get install cryptsetup When I boot, the system says (try to translate) that either the partition is not found or is not ready. I should wait, press M for manual or S to jump over. What am I missing here?

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• old ssl certficate didn't go away on apache2

  - by user1212143

  I have replaced the old ssl certficate with new one and restart apache several time but the old certificate still show on web browser and when I run a command openssl s_client -connect 127.0.0.1:443 -showcerts also I have delete all old certficate files. so not sure where apache still read these certficate. and not read the new one. here is my ssl.conf Listen 0.0.0.0:443 SSLEngine on SSLOptions +StrictRequire <Directory /> SSLRequireSSL </Directory> SSLProtocol -all +TLSv1 +SSLv3 SSLCipherSuite HIGH:MEDIUM:!aNULL:+SHA1:+MD5:+HIGH:+MEDIUM SSLMutex file:/usr/apache2/logs/ssl_mutex SSLRandomSeed startup file:/dev/urandom 1024 SSLRandomSeed connect file:/dev/urandom 1024 SSLSessionCache shm:/usr/apache2/logs/ssl_cache_shm SSLSessionCacheTimeout 600 SSLPassPhraseDialog builtin SSLCertificateFile /usr/apache2/conf/ssl.crt/server.crt SSLCertificateKeyFile /usr/apache2/conf/ssl.key/server.key SSLVerifyClient none SSLProxyEngine off <IfModule mime.c> AddType application/x-x509-ca-cert .crt AddType application/x-pkcs7-crl .crl </IfModule>

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• Why does changing a truecrypt password take such a long time?

  - by Alex

  I am changing the password of a truecrypt file container. This takes around 1 minute. Why? time truecrypt --text --change /tmp/user1.tc --keyfiles= --new-keyfiles= --password=known --new-password=known --random-source=/dev/null" If I use strace I see that it basically does not do anything: it simply reads lots of random data from /dev/urandom (even if i specified /dev/null as random source) and finally changes the password: open("/dev/urandom", O_RDONLY) = 6 read(6, "\36&{\351\212\212\343\202\34\313\242\312I\326\235\245\224\300\354O)\270Q\200 \201J\227\224\311_\212\367"..., 640) = 640 close(6) = 0

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• how can i find my usb2rs232 driver

  - by mefmef

  i have a device that is correctly connected to my PC . but i could not see it in /dev . what does it means? is it because of not installing my drive? $ /dev ls before connecting my device: agpgart mei sda1 tty28 tty59 ttyS30 autofs mem sda2 tty29 tty6 ttyS31 block net sda5 tty3 tty60 ttyS4 bsg network_latency sda6 tty30 tty61 ttyS5 btrfs-control network_throughput serial tty31 tty62 ttyS6 bus null sg0 tty32 tty63 ttyS7 char oldmem shm tty33 tty7 ttyS8 console parport0 snapshot tty34 tty8 ttyS9 core port snd tty35 tty9 ttyUSB0 cpu ppp stderr tty36 ttyprintk uinput cpu_dma_latency psaux stdin tty37 ttyS0 urandom disk ptmx stdout tty38 ttyS1 usbmon0 dri pts tty tty39 ttyS10 usbmon1 ecryptfs ram0 tty0 tty4 ttyS11 usbmon2 fb0 ram1 tty1 tty40 ttyS12 vcs fd ram10 tty10 tty41 ttyS13 vcs1 full ram11 tty11 tty42 ttyS14 vcs2 fuse ram12 tty12 tty43 ttyS15 vcs3 hidraw0 ram13 tty13 tty44 ttyS16 vcs4 hpet ram14 tty14 tty45 ttyS17 vcs5 input ram15 tty15 tty46 ttyS18 vcs6 kmsg ram2 tty16 tty47 ttyS19 vcsa log ram3 tty17 tty48 ttyS2 vcsa1 loop0 ram4 tty18 tty49 ttyS20 vcsa2 loop1 ram5 tty19 tty5 ttyS21 vcsa3 loop2 ram6 tty2 tty50 ttyS22 vcsa4 loop3 ram7 tty20 tty51 ttyS23 vcsa5 loop4 ram8 tty21 tty52 ttyS24 vcsa6 loop5 ram9 tty22 tty53 ttyS25 vga_arbiter loop6 random tty23 tty54 ttyS26 zero loop7 rfkill tty24 tty55 ttyS27 lp0 rtc tty25 tty56 ttyS28 mapper rtc0 tty26 tty57 ttyS29 mcelog sda tty27 tty58 ttyS3 $ /dev ls after connecting my device: agpgart mei sda1 tty28 tty59 ttyS30 autofs mem sda2 tty29 tty6 ttyS31 block net sda5 tty3 tty60 ttyS4 bsg network_latency sda6 tty30 tty61 ttyS5 btrfs-control network_throughput serial tty31 tty62 ttyS6 bus null sg0 tty32 tty63 ttyS7 char oldmem shm tty33 tty7 ttyS8 console parport0 snapshot tty34 tty8 ttyS9 core port snd tty35 tty9 ttyUSB0 cpu ppp stderr tty36 ttyprintk ttyUSB1 cpu_dma_latency psaux stdin tty37 ttyS0 uinput disk ptmx stdout tty38 ttyS1 urandom dri pts tty tty39 ttyS10 usbmon0 ecryptfs ram0 tty0 tty4 ttyS11 usbmon1 fb0 ram1 tty1 tty40 ttyS12 usbmon2 fd ram10 tty10 tty41 ttyS13 vcs full ram11 tty11 tty42 ttyS14 vcs1 fuse ram12 tty12 tty43 ttyS15 vcs2 hidraw0 ram13 tty13 tty44 ttyS16 vcs3 hpet ram14 tty14 tty45 ttyS17 vcs4 input ram15 tty15 tty46 ttyS18 vcs5 kmsg ram2 tty16 tty47 ttyS19 vcs6 log ram3 tty17 tty48 ttyS2 vcsa loop0 ram4 tty18 tty49 ttyS20 vcsa1 loop1 ram5 tty19 tty5 ttyS21 vcsa2 loop2 ram6 tty2 tty50 ttyS22 vcsa3 loop3 ram7 tty20 tty51 ttyS23 vcsa4 loop4 ram8 tty21 tty52 ttyS24 vcsa5 loop5 ram9 tty22 tty53 ttyS25 vcsa6 loop6 random tty23 tty54 ttyS26 vga_arbiter loop7 rfkill tty24 tty55 ttyS27 zero lp0 rtc tty25 tty56 ttyS28 mapper rtc0 tty26 tty57 ttyS29 mcelog sda tty27 tty58 ttyS3

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• checksecurity / setuid changes, is this a bug or did somebody break in?

  - by Fabian Zeindl

  I received a mail by checksecurity from my ubuntu 12.04 server with the following content: --- setuid.today 2012-06-03 06:48:09.892436281 +0200 +++ /var/log/setuid/setuid.new.tmp 2012-06-17 06:47:51.376597730 +0200 @@ -30,2 +30,2 @@ - 131904 4755 2 root root 71280 Wed May 16 07:23:08.0000000000 2012 ./usr/bin/sudo - 131904 4755 2 root root 71280 Wed May 16 07:23:08.0000000000 2012 ./usr/bin/sudoedit + 143967 4755 2 root root 71288 Fri Jun 1 05:53:44.0000000000 2012 ./usr/bin/sudo + 143967 4755 2 root root 71288 Fri Jun 1 05:53:44.0000000000 2012 ./usr/bin/sudoedit @@ -42 +42 @@ - 130507 666 1 root root 0 Sat Jun 2 18:04:57.0752979385 2012 ./var/spool/postfix/dev/urandom + 130507 666 1 root root 0 Mon Jun 11 08:47:16.0919802556 2012 ./var/spool/postfix/dev/urandom First i was worried, then i realized that the change was actually 2 weeks ago, i think there was a sudo-update back then. Since checksecurity runs in /etc/cron.daily i wondered why i only get that email now. I looked into /var/log/setuid/ and found the following files: total 32 -rw-r----- 1 root adm 816 Jun 17 06:47 setuid.changes -rw-r----- 1 root adm 228 Jun 3 06:48 setuid.changes.1.gz -rw-r----- 1 root adm 328 May 27 06:47 setuid.changes.2.gz -rw-r----- 1 root root 1248 May 20 06:47 setuid.changes.3.gz -rw-r----- 1 root adm 4473 Jun 17 06:47 setuid.today -rw-r----- 1 root adm 4473 Jun 3 06:48 setuid.yesterday The obvious thing that confuses me is that the file setuid.yesterday is not from yesterday = Jun/16. Is this a bug?

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• Forcing smtp outgoing mail encryption on postfix

  - by Simon

  Hi all, anyone knows how to tell postfix to encrypt outgoing mail? I have configured it to use encryption on reception, but I´m unnable to do it with the out mail. This is my main.cf file: smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination smtpd_sasl_auth_enable = yes smtpd_sasl_path = smtpd transport_maps = hash:/etc/postfix/transport # tls config smtp_use_tls = yes smtpd_use_tls = yes smtp_tls_note_starttls_offer = yes smtpd_tls_key_file = /etc/postfix/ssl/smtpd.pem smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.pem smtpd_tls_CAfile = /etc/postfix/ssl/smtpd.pem smtpd_tls_loglevel = 1 smtpd_tls_received_header = yes smtpd_tls_session_cache_timeout = 3600s tls_random_source = dev:/dev/urandom Thanks in advance!

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• Forcing smtp outgoing mail encryption on postfix

  - by Simon

  Hi all, anyone knows how to tell postfix to encrypt outgoing mail? I have configured it to use encryption on reception, but I´m unnable to do it with the out mail. This is my main.cf file: smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination smtpd_sasl_auth_enable = yes smtpd_sasl_path = smtpd transport_maps = hash:/etc/postfix/transport # tls config smtp_use_tls = yes smtpd_use_tls = yes smtp_tls_note_starttls_offer = yes smtpd_tls_key_file = /etc/postfix/ssl/smtpd.pem smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.pem smtpd_tls_CAfile = /etc/postfix/ssl/smtpd.pem smtpd_tls_loglevel = 1 smtpd_tls_received_header = yes smtpd_tls_session_cache_timeout = 3600s tls_random_source = dev:/dev/urandom Thanks in advance!

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• smtpd_tls_auth_only exclude 127.0.0.1

  - by Pol Hallen

  I configurated postfix to force uses TLS. When an external client try to send an email using this server there is not any problems. But using webmail (127.0.0.1) postfix wants TLS: delivery temporarily suspended: TLS is required, but was not offered by host 127.0.0.1[127.0.0.1]) Which changes I need to do to master.cf? smtp_use_tls = yes smtp_tls_security_level = encrypt smtpd_use_tls = yes smtpd_tls_auth_only = yes smtpd_tls_key_file = /etc/postfix/ssl/xxx.key smtpd_tls_cert_file = /etc/postfix/ssl/xxx.crt smtpd_tls_loglevel = 1 smtpd_tls_received_header = yes smtpd_tls_session_cache_timeout = 3600s tls_random_source = dev:/dev/urandom smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache

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• How to rate-limit a pipe under linux ?

  - by Frédéric Grosshans

  Is there a filter which I could use to rate-limit a pipe on linux? If this exists, let call it rate-limit, I want to be able to type in a terminal something like cat /dev/urandom | rate-limit 3 -k | foo in order to send a a stream of random bytes to foo's standard input at a rate (lower than) 3 kbytes/s.

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• Example about crypto/rand in Go

  - by nevalu

  Could put a little example about the use of crypto/rand [1]? The function Read has as parameter an array of bytes. Why? If it access to /dev/urandom to get the random data. func Read(b []byte) (n int, err os.Error) [1] http://golang.org/pkg/crypto/rand/

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• Rails on Google App Engine - Error on OS X development machine

  - by Phillip Parker

  Hi, I'm running through the Ruby on Rails tutorial at http://guides.rubyonrails.org/getting_started.html (adjusting where appropriate for Google's App Engine). All is well up till section 6.3: when I try to click "New Post", I get the following error: Internal Server Error (500) Request Method: GET Request URL: http://localhost:8080/500.html access denied (java.io.FilePermission /dev/urandom read) It works fine when I upload the application to Google's App Engine; it's just on my development machine (OS X 10.6) that it doesn't work. Thanks in advance.

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• Random number from a range in a Bash Script

  - by Jack

  Hi, I need to generate a random port number between 2000-65000 from a shell script. The problem is $RANDOM is only a 16bit number, so im stuck! PORT=$(($RANDOM%63000+2001)) would work nicely if it wasn't for the size limitation. Does anyone have an example of how I can do this, maybe by extracting something from /dev/urandom and getting it within a range? Thanks.

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• TS-7800 Hangs on bootup

  - by Reid

  I have a TS-7800, and it typically boots from the SD card inserted in it. When I tried to boot it up today, it hung on the syslog line. I am now having "Read only file system" problems. What has gone wrong? Bootup console: >> Copyright (c) 2008, Technologic Systems >> Booting from SD card... . . . . >> Booting to SD Card... INIT: version 2.86 booting Starting the hotplug events dispatcher: udevd. Synthesizing the initial hotplug events...done. Waiting for /dev to be fully populated...done. mount: can't find / in /etc/fstab or /etc/mtab Cleaning up ifupdown...rm: cannot remove `/etc/network/run/ifstate': Read-only file system Loading kernel modules...done. Checking all file systems... fsck 1.37 (21-Mar-2005) ... done. none on /dev/pts type devpts (rw,gid=5,mode=620) /etc/init.d/rcS: line 39: /tmp/.clean: Read-only file system Setting up networking...done. Setting up IP spoofing protection: rp_filter. Enabling packet forwarding...done. Configuring network interfaces...ifup: failed to open statefile /etc/network/run/ifstate: Read-only file system done. Starting portmap daemon: portmap. /etc/init.d/rcS: line 39: /tmp/.clean: Read-only file system /etc/init.d/rcS: line 24: /var/run/utmp: Read-only file system rm: cannot remove `/var/lib/urandom/random-seed': Read-only file system urandom start: failed. Recovering nvi editor sessions... done. INIT: Entering runlevel: 3 Starting system log daemon: syslogd . Starting kernel log daemon: klogd. Starting MTA: open: Read-only file system touch: cannot touch `/var/lib/exim4/config.autogenerated.tmp': Read-only file system chown: cannot access `/var/lib/exim4/config.autogenerated.tmp': No such file or directory chmod: cannot access `/var/lib/exim4/config.autogenerated.tmp': No such file or directory chmod: changing permissions of `/var/lib/exim4/config.autogenerated': Read-only file system /usr/sbin/update-exim4.conf: line 260: cannot create temp file for here document: Read-only file system /usr/sbin/update-exim4.conf: line 387: /var/lib/exim4/config.autogenerated.tmp: Read-only file system 2002-01-01 01:31:36 Cannot open main log file "/var/log/exim4/mainlog": Read-only file system: euid=0 egid=0 2002-01-01 01:31:36 non-existent configuration file(s): /var/lib/exim4/config.autogenerated.tmp 2002-01-01 01:31:36 Cannot open main log file "/var/log/exim4/mainlog": Read-only file system: euid=0 egid=0 exim: could not open panic log - aborting: see message(s) above Invalid new configfile /var/lib/exim4/config.autogenerated.tmp not installing /var/lib/exim4/config.autogenerated.tmp to /var/lib/exim4/config.autogenerated Starting internet superserver: inetd. Starting OpenBSD Secure Shell server: sshd. Starting NFS common utilities: statdStarting periodic command scheduler: cron/usr/sbin/cron: can't open or create /var/run/crond.pid: Read-only file system . Starting web server (apache2)...(30)Read-only file system: apache2: could not open error log file /var/log/apache2/error.log. Unable to open logs failed! Debian GNU/Linux 3.1 ts7800 ttyS0 ts7800 login:

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• Linux process management

  - by tanascius

  Hello, I started a long running background-process (dd with /etc/urandom) in my ssh console. Later I had to disconnect. When I logged in, again (this time directly, without ssh), the process still seemed to to run. I am not sure what happened - I did not use disown. When I logged in later, the process was not listed in top at first, but after a while it reclaimed a high CPU percentage, as I expected. So I assume dd is still running. Now, I'd like to see the progress. I use kill -USR1 <pid> but nothing is printed. Is there any way to get the output again?

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