[Samsung Galaxy Nexus] envidia:
I did:

[B]# ./fastboot oem unlock[/B]
[B]# ./fastboot boot recovery-clockwork-6.0.1.0-maguro.img[/B]

And now adb is working. I get a root shell, but maybe that's normal from CWM recovery.

[B]~ # whoami [/B]
root

If I delete the update file inside the cache folder, it appers again in the next reboot. I don't understand why.

[B]~ # ls[/B]
boot etc sdcard
cache init sys
charger init.rc system
data proc tmp
datadata res ueventd.goldfish.rc
default.prop root ueventd.rc
dev sbin ueventd.tuna.rc
emmc sd-ext
[B]~ # ls /cache/[/B]
5a81769b6d01.signed-yakju-IMM76I-from-ICL53F.5a81769b.zip
lost+found
recovery
[B]~ # rm /cache/5a81769b6d01.signed-yakju-IMM76I-from-ICL53F.5a81769b.zip [/B]
[B]~ # ls /cache/[/B]
lost+found recovery

In /tmp there's a recovery log:

[B]~ # cat tmp/recovery.log [/B]
Starting recovery on Sat Jan 1 00:11:21 2000
can't open /dev/tty0: No such file or directory
framebuffer: fd 3 (720 x 1280)
ClockworkMod Recovery v6.0.1.0
recovery filesystem table
=========================
0 /tmp ramdisk (null) (null) 0
1 /sdcard datamedia /dev/null (null) 0
2 /system ext4 /dev/block/platform/omap/omap_hsmmc.0/by-name/system (null) 0
3 /cache ext4 /dev/block/platform/omap/omap_hsmmc.0/by-name/cache (null) 0
4 /data ext4 /dev/block/platform/omap/omap_hsmmc.0/by-name/userdata (null) 0
5 /misc emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/misc (null) 0
6 /boot emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/boot (null) 0
7 /recovery emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/recovery (null) 0
8 /sbl emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/sbl (null) 0
9 /xloader emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/xloader (null) 0
10 /radio emmc /dev/block/platform/omap/omap_hsmmc.0/by-name/radio (null) 0

W:Unable to get recovery.fstab info for /datadata during fstab generation!
W:Unable to get recovery.fstab info for /emmc during fstab generation!
W:Unable to get recovery.fstab info for /sd-ext during fstab generation!
I:Completed outputting fstab.
I:Processing arguments.
I:Boot command: boot-recovery
I:Got arguments from boot message
I:Checking arguments.
I:device_recovery_start()
Command: "recovery" "--update_package=/cache/5a81769b6d01.signed-yakju-IMM76I-from-ICL53F.5a81769b.zip"

ro.secure=1
ro.allow.mock.location=0
ro.debuggable=1
persist.sys.usb.config=mtp,adb
ro.build.id=IMM76L
ro.build.display.id=cm_maguro-userdebug 4.0.4 IMM76L eng.koush.20120718.160329 test-keys
ro.build.version.incremental=eng.koush.20120718.160329
ro.build.version.sdk=15
ro.build.version.codename=REL
ro.build.version.release=4.0.4
ro.build.date=Wed Jul 18 16:04:55 PDT 2012
ro.build.date.utc=0
ro.build.type=userdebug
ro.build.user=koush
ro.build.host=Koushik-Lion.local
ro.build.tags=test-keys
ro.product.model=Galaxy Nexus
ro.product.brand=Google
ro.product.name=yakju
ro.product.device=maguro
ro.product.board=tuna
ro.product.cpu.abi=armeabi-v7a
ro.product.cpu.abi2=armeabi
ro.product.manufacturer=Samsung
ro.product.locale.language=en
ro.product.locale.region=US
ro.wifi.channels=
ro.board.platform=omap4
ro.build.product=maguro
ro.build.description=yakju-user 4.0.4 IMM76I 330937 release-keys
ro.build.fingerprint=google/yakju/maguro:4.0.4/IMM76I/330937:user/release-keys
ro.build.characteristics=nosdcard
ro.cm.device=maguro
rild.libpath=/vendor/lib/libsec-ril.so
rild.libargs=-d /dev/ttys0
telephony.lteOnCdmaDevice=0
ro.telephony.call_ring.multiple=0
ro.rommanager.developerid=cyanogenmod
keyguard.no_require_sim=true
ro.url.legal=http://www.google.com/intl/%s/mobile/android/basic/phone-legal.html
ro.url.legal.android_privacy=http://www.google.com/intl/%s/mobile/android/basic/privacy.html
ro.com.google.clientidbase=android-google
ro.com.android.wifi-watchlist=GoogleGuest
ro.setupwizard.enterprise_mode=1
ro.com.android.dateformat=MM-dd-yyyy
ro.com.android.dataroaming=false
ro.cm.version=9-20120718-UNOFFICIAL-maguro
ro.modversion=9-20120718-UNOFFICIAL-maguro
ro.config.ringtone=CyanTone.ogg
ro.config.notification_sound=CyanMessage.ogg
ro.config.alarm_alert=CyanAlarm.ogg
wifi.interface=wlan0
wifi.supplicant_scan_interval=15
ro.opengles.version=131072
ro.sf.lcd_density=320
dalvik.vm.heapstartsize=8m
dalvik.vm.heapgrowthlimit=64m
dalvik.vm.heapsize=256m
dalvik.vm.lockprof.threshold=500
dalvik.vm.dexopt-flags=m=y
net.bt.name=Android
net.change=net.bt.name
dalvik.vm.stack-trace-file=/data/anr/traces.txt
ro.factorytest=0
ro.serialno=0149C25E0200A00B
ro.bootmode=unknown
ro.baseband=I9250XXKK6
ro.carrier=unknown
ro.bootloader=PRIMEKK15
ro.hardware=tuna
ro.revision=9
ro.emmc=0
init.svc.recovery=running
service.adb.root=1
init.svc.adbd=running

Finding update package...
I:Update location: /cache/5a81769b6d01.signed-yakju-IMM76I-from-ICL53F.5a81769b.zip
Opening update package...
I:1 key(s) loaded from /res/keys
Verifying update package...
I:comment is 1604 bytes; signature 1586 bytes from end
E:failed to verify whole-file signature
I:verify_file returned 1
E:signature verification failed

Maybe it's a permissions problem, like if the filesystem is mounted read only, so the changes get reverted at every boot.

What else could I try now that I have a shell?

Thanks guys.